There are a number of nice extras that overalls offer for securing someone:

• You can weave the straps through e.g. a chair or a clothesline before locking, so that the straps fixate the wearer to it.
  See also Ariel in Gray Skirtalls.
• The straps are also nice points to attach wandering hands to, esp. in the back.
  See also Ariel in Black PVC Overalls and Ariel in Blue Suede Overalls.
  Belt loops are nice fixation points, too.
• Some overalls have straps at the side of the waist, to regulate the width a bit. If you're lucky, these are the right size to hold the wearer's wrist, without being able to retract the hands through. The same can be done with side buttons: just find two that are at the right distance, close them with the wrist in between, and the hands are caught.
  See also Ariel in Black PVC Overalls.
  You can also make a construction in the pockets to trap the hands. The company o.g. style sells clothes with such special pockets. (Page is in German, but just scroll down to the 'Handfixierung in der Tasche'.)
• Yet another way to disable the hands would be to use (locking) mittens, which you can find at bondage shops (like the shop above) or adult baby sites.
  See also Ariel in Blue Corduroy Overalls.
• If the garment has long legs, you can connect the hems to hobble the wearer. Even more effective is a zipper on the inside of the legs, that fixates both legs together when closed. There are even straight-overalls available with straps around the legs (see the 'Overalls Links' page, shop section.)
  In Ariel in Scenario: Committed, gallery 2, her suit has small loops at the ankles that can be locked together.

Here are 2 ideas that a guy named Tigon at the Overalls Forum suggested:

• The first idea is to have a person in bibs, and under their bibs at the waist is a belt, ideally locking, even better with straps through the leg to make it like a harness, nice and secure. Have d-rings secure on the sides of the belt, by the side buttons of the overalls. The person is also to wear wrist cuffs, ideally locking (when I did this i had a long sleeve shirt that covered the cuffs). Next you want to use either a lock or zip tie, or lock to connect the cuffs to the belt though the gaps between the side buttons. Once it is all tight and the person puts their hands in their pockets, they are going to just look like they are walking around with hands in their overalls pockets. In reality, they cannot move their hands from their waist. Additionally this can be further complicated by having similar cuffs on the upper arms (under a shirt with a small hold in the sides), and similarly connected to a harness/belt going around the chest.
  Note from me: it might be least obvious if you use locking bracelets around the wrists, like the Love Bracelets Ariel demonstrates in Purple Velvet Overalls.
• The second one is similar and much simpler but much harder to get out of. I had a friend help me test this one. She came over and I was wearing shortalls and a onesie (because why not). I then put my hands in my pockets, and from inside the bibs, around the pocket itself at my wrists, she tightened a zip tie (cuffs would also work). So when they were nice and snug, I could not pull my hands out of my pockets. She then took me around to some shops here she had some errands to run. All the while I was walking along in shortalls with seemingly just my hands in my pockets. Totally helpless.
  Note from me: This should work with any type of bottom with deep pockets, but of course overalls are the best ;-)