Can't imagine why i never thought of this before. A very simple way to deny yourself access to a key for a few hours : tie it securely in a cloth and put it in the washing machine on a long wash. I've never really taken much notice of how long a full wash takes until today. My machine counts down from 1hr 40mins. I knew it started counting again when it switches to drying mode but it was a bit of (quite nice) shock when it announced I'd be locked for another 3 hrs 50mins.