What stinks about the whole thing (no I didn't have anyone make a key to my lock but have had trespassers) is that...even if you file a formal complaint a warning is as far as the first complaint will go. Call your sherriff and file that complaint though because the next time you catch them they will be issued a ticket...I'd say after that you would have a stronger leg to stand on.

Good luck!! I'm thinking change the locks, but it really isn't going to solve things.