Clothes like jumpers (or skirtalls) can look like overalls, but with a skirt in stead of pants.

Skortall with flap closed, hiding the shorts Skortall with shorts exposed; padlock hides behind flap

A skortall has skorts at the bottom, meaning shorts that look like a skirt when worn, either because they're so wide, or because a flap in front makes them look like a skirt. In the pictures you can see how convenient the front flap is in hiding a padlock beneath, making this ideal for public bondage. But of course this is not really a skirted garment :) See also Ariel in White Skortalls.

With a real skirt at the bottom, there is the additional risk that the victim can pull the garment over her (his?) head. A few things can be done against that:

The leather strap closes and locks between the legs

You can fix a belt to the front and back waist of the jumper that passes under the crotch when fastened. (Attaching it at waist height makes the skirt still fall naturally, if you're interested in making it inconspicuous.) In case the jumper is not meant to be pulled over the head, it can be a fixed belt, but if over the head is the only way to get out of it, it needs to be a belt with a buckle or other fastening, like in the illustration. Then just close and lock the belt after putting the jumper on, and the victim is secure. Note that the position of the buckle is closely related to the comfort in wearing the jumper...

Other options include:

• Attach panties to prevent lifting over the head.
• Either get a skirt that is too tight to lift past the shoulders (hobble skirt / hobble dress), or make it so. With long skirts the split can be zipped or sewn shut.