Unlock wide variety of locks with a bumping(rapping) key.
I didn’t try this, but it seems like a good idea. They claim you can open 90% of all locks with this technique.
All you need is an existing key that fits the target lock, a metal file and something to hit the key.. To see how to do it, you can find a video and pdf and video at: toool.nl.
There is bump proof locks, they are more expensive than your regular hardware store locks but I think it’s worth it. You can find a list here (PDF).