For the house, I have a set of keys hidden in an outbuilding, inside an electrical box. If someone finds it, they've earned their reward, which is a close encounter with the Great Danes that live indoors.

Standard procedure for cars is a spare key in my wallet and a spare key in DW's purse.

I've always been leery of the magnetic box thing; prospective joyriders are known to troll parking lots and check bumpers for these.

But I may need to reconsider. A couple of days ago, DW managed to lock her keys in a running car, and the spare key had migrated somewhere else (south for the winter, presumably). I therefore went for a drive -- can't resist a damsel in distress.

So: where's a good place to hide a key/magnetic box that's not readily found by vandals on a fishing expedition?