A tie wrap securing a side-release buckle A tie wrap around a button and through the buttonhole	tie wraps Since there is a pretty wide diversity of fastenings, there is not much to say in general, but one thing that works on a number of fastenings is tie wraps: in principle one can often be used instead of a padlock, but also to prevent side-release and push button buckles. If you choose a tie wrap in the right color, and cut the loose end off, it will not be obvious. Of course tie wraps can only be used when the wearer has no access to scissors or cutters, or the tie-wrap itself is out of reach. And even then with a tie-wrap everyone can release the wearer, while with a padlock only the keyholder can. A few things to keep in mind though: make sure you can reach the tie wrap to cut it: for instance with the regular overalls hooks, a tight tie wrap will be mostly covered by the button, and you won't get at it easily. To secure button-and-hole fastenings, make sure you include the side of the hole in the tie wrap. (Like with 2nd picture.)
For button straps use the same method as with other buttons A padlock around button and through buttonhole	Standard button-and-hole The simplest type: a button on the strap, and a hole in the bib, or reverse. To Lock: put a padlock around the base of the button as illustrated in the picture for a side button. The loop (shackle) of the lock must be just a bit smaller than the button. If the shackle is just a bit too large, you might include the fabric between button hole and edge. See for the same technique: Ariel in White Skortalls, but with the waist button. To fix permanently: close the button, and sew the buttonhole closed so far, that the button can't pass through anymore. This is almost invisible.
	Standard hook-and-button The most regular type: a metal wire bent to have a button hooked into it, on the strap, and a button on the bib.
	To lock: get a padlock that is small enough that the button doesn't fit through the hoop. Hook the fastening up, and lock it around the wire just above the button, as the pictures show. See for example Ariel in Scenario: Retarded, gallery 1 and 2. Note that when you use zip ties around the smallest part of the hook, that might be as effective as padlocks in preventing them from opening, but they will be quite hard to remove again since the button will be in the way of reaching them with scissors.
	To make sturdier: wind thin wire around the end. This is useful for the buckles that have a seperate end piece that might disconnect from the buckle wires when more strain is put on the straps. This idea and the picture comes from contributor Overalls Decay (e.g. at DeviantArt), who uses it to hang from his overalls straps. I would still advice against suspending someone from their overalls straps, since they are not contructed for that, but if you make sure the person doesn't get hurt when something gives and (s)he falls down, this could help.
	To fix permanently: hook it up, and bend the wires above the button towards each other until the button can't fit through anymore. (Note that this doesn't work if you have a hook containing two parts of wire and a center piece, like in the picture above.) You can even close the buckle with the strap twisted half a turn, and then twist the upper part back, so that the wire wraps tightly around the stem of the button.
	Plate and Slit This is an alternative overalls hook, which is used by Carrhart and others. It's a metal plate that is inserted to a slit sideways, and then twisted back. See also Ariel in Scenario: Committed, gallery 1.
Since the plate needs the whole width of the slot, any lock will block it from opening	To lock: put a padlock through the slit: since the slit is not much wider than the plate, this is enough to prevent the plate from going though. Note that while most overalls buckles are hard to undo with only one hand, these are particularly challenging, so if you disable one hand, or put the overalls on backward (as in the Committed gallery), they are hard to escape from even without any locks.
	Fireman's clip A hoop closing with a springed bar on the strap, a hole in the bib. To Lock: The clip itself is hard to lock, but you can put a padlock through the hole in the bib, and where the clip is attached to the strap. To fix permanently: you can probably prevent the bar of the clip from retreating by squeezing above the lever with pliers.
	Belt buckle A buckle with a pin through a hole in the strap. (Guess you know this one) To Lock: Easiest is to put a padlock through a lower hole on the strap. If the padlock is big enough, it won't fit through the buckle. If you need the last hole, you can probably put the padlock though that hole, possibly leaving the buckle pin out. To fix permanently: sew the strap to buckle or bib.
	Weaving buckle or D-rings One buckle without a pin, or two D-rings, through which the strap is woven. To Lock: not so easy without alteration, since there is nothing on the strap to affix to. You can make an inconspicuous hole in the strap beyond the buckle though, to put a lock through. For hiding: If you weave the strap through the flipped buckle, the strap end will be on the inside and the lock can be hidden by the bib or the strap. To fix permanently: sew the strap to buckle or bib.
	velcro two pieces of material that stick together when connected. To Lock: not so easy without alteration, since there is nothing on the straps to affix to. You can make an inconspicuous hole in the straps beyond the buckle though, to put a lock through both. To fix permanently: sew the straps together.
	Side release buckle (Fastex buckle) A plastic buckle that closes with a nice click, and you need to press on both sides to open again. To Lock: drill or file one or two inconspicuous holes in the extruding sides of the inner part: you can put a padlock through them. See also Ariel in Gray Skirtalls. To fix permanently: you can probably glue or jam the buckle. If you search the web for locking fastex buckle or locking side release buckle, you can also find buckles that lock with a (primitive) key, with a 2 or 3 digit combination, or with an extra button ('triple lock'), so that you need two hands to undo it. (Might be secure enough for buckles at the back, like used on this safety harness.)
	Front release buckle (like on ski overalls) A plastic buckle that closes with a nice click, and you need to press the button in the center to open again. To Lock: you might be able to drill a hole in the middle for a padlock (with a longer hasp), but you risk the plastic cracking. These pictures show a low security alternative: if you can make a plate the covers or wraps around the front of the buckle, and make a small hole in it, the buckle can't be opened with your bare hands anymore, and you'll need a suitable tool to press the button. When you customize the shape of the hole, you can make it require a specific tool that fits deep enough and you can exert enough force with to depress the button. As a proof-of-concept I cut out a piece of plastic from a disposable food container, which I fixed to the buckles with cellotape. (Somehow my efforts with superglue didn't stick - perhaps I should have cleaned the surfaces first.) See also Ariel in Ski Overalls.
	Snaps (UK: Press Studs) you know, those things you press together and they close, if you're lucky. To Lock: can't think of a way. Just replace them with something useful. To fix permanently: sew the surrounding cloth together. A Japanese webshop for Adult Babies seems to sell gear with a sort of snaps that require a magnet to undo, probably similar to the Segufix locks (see below). They have a romper with 16 locking snaps, and also mittens, a bib and diaper pants. (From what I can understand using automatic translation.) These snaps don't look like they are locking, so would be ideal for public bondage, but I have no idea if they are available separately.

Already locking fasteners

There are also some specific, already locking clips, that you can use replace less useful fasteners:

	Locking handbag clips Some purses, handbags and suitcases have locking clips. Either try to rescue some off old bags, or try to find a shop that sells them separately. See also Ariel in Denim Skortalls.
	Psychiatric ward locks There are some companies that make restraints for psychiatric patients. They use something that roughly compares big snaps, but need a spiked or magnetic key put over the top to pull them apart again. You can order the locks from companies like Heetkamp (Dutch), or Segufix (English, German, and several other languages).
	Locking Side Release Buckles They are not that easy to find, but there are side release buckles that have a locking mechanism: there are ones with a key, and ones that require a number combination. There are even ones that require a magnet to be able to press the side buttons (see below). One place I found that sells the key lock buckles is plastic-buckle.com, but like the combination buckle they look a bit big for overalls straps. For key lock buckles it is almost easier and cheaper to buy a locking toddler wrist leash or harness from China (e.g. search eBay; already from just over 5 euro; harness around 10 for 3 buckles), and take the buckles off that.
	Magnetic Locking Buckles Apart from the wrist leashes and harnesses with key-locking buckles, there are also variants with magnetic locking buckles. The interesting things about these buckles is of course that without a keyhole, they don't look like they lock, and an unsuspecting wearer might close them without realizing how to open them again. (You don't need the magnet to lock them.) I have by now found one place where you can buy the side-release buckles separately: search on Aliexpress.com for "lock key paracord" and look for the offers by CooBigo. (You can buy them in different quantities, like 1, 2, 5, 10, and 50, but unluckily in slightly differently-named shops. And even though the description is equal for each quantity, I haven't been able to find all of them with one search (great search engine :-P ), so you may have to try different combinations of terms.) That seller also seems to be active on eBay.com now as fashionland88; search e.g. for 'locking' in Crafts > Sewing > Closures & Connectors > Buckles & Straps. Otherwise just buy two wrist leashes, strip the buckles off them, and attach them to a pair of overalls. The photo's show my first prototype (with the other type of buckle), and it can be improved on to make it look less conspicuous. See these shortalls in action in: Ariel and the Trick Buckles. If you want to do this yourself, I wrote a list of steps to help you.