A fantasy is a terrible thing to waist (locking of course) !
All locking devices MUST be at the rear of the waist band ! Makes it more difficult to escape timely to prevent the inevitable use of the diapers within.
You could experiment with a combination lock(s). No keys here but you will have to solve the combination before your body times out and the diapers are used for their intended purpose. You could start with the small luggage locks with 3 cylinder rows and 6 numbers in each and solve these quite quickly. At 4 cylinders the element of the time factor increases. With 4 cylinders and 0-9 numbers now you really have a challenge on your hands.
"Did I just say hands?" With the hands immobilized in locked on mittens you need to really be talented to solve that removal step. Perhaps at this time it would be a good idea to have a partner to make matters just that much worse !
With the hands in locking mittens now you not only have to solve the combination lock(s) but have to find a way to remove the mittens to solve the combination step.
Now you could hide or place the mittens keys; if using keys, anywhere requiring a time element to go to that location to retrieve the keys and start to unravel this conundrum !
Alternate scenario to this puzzle by adding a locking collar with a "D" ring to lock another combination lock with the mitten keys onto the "D" ring. Now in an emergency the keys for release are nearby but need to be manipulated to remove the mittens to have the hands free to solve the combination lock locking the diaper cover on. The more time delaying tactics will insure a very wet and perhaps messy diaper prison.
Also consider wearing a locking Babydoll nighty or similiar short dress just exposing the locking diaper cover. Then add locking mary jane shoes with cute sox with lace appliques or thigh high hold-ups in a pastel (pink) color. Endless humiliation.
Another scenario is the use of jingle bells - lots and lots of them. Attached them to the locking collar; locking baby doll/dress; on the mittens; in several places about the locking waist band of the diaper cover. Now you will not go quietly trying to escape your diaper prison.
A fantasy is a horrible thing to waist (locking of course) - ENJOY !