I don't see why it's an exploit. It's a strategy. Just make it a high level spell and a rare scroll.
Well, it could be thought of that way, but I agree with the others that it could make the game unbalanced. Still, if lock bashing was an option, or if guards had "Skeleton Keys" of their own then there would be nothing to exploit. Perhaps lock could be a spell only cast while not in active combat. Perhaps it can have a mini-game like picking locks did in Oblivion (seems stupid but I'm just throwing out ideas). I DON'T CARE! I just want to be able to lock my own damn house from a RP angle.
Back to the topic of dropped gold. I don't need every little thing to be havok enabled. Even if the gold were to have physics, I would still like to have different sized piles of gold to drop. Something about that was just so awesome to me, even more so when I can lock the room behind me and say "Good, my lewt is secure".