Help finding old story

I’m trying to find an old story that I can’t remember the title of or find a link to. A woman locks herself into chastity and either loses the key or doesn’t have the key. She ends up going to a locksmith who is able to remove the lock, but he ends up replacing the lock with a more secure one he has the key too and she has signed a control that he maintains control over her belt. Please help me find it.