You might try getting some of that steel cable at Tractor Supply and using it to "anchor" your cache to it's location. Granted, it would be easier to find, but the perp isn't going to be getting away with it without some cutting pliers.
Another option could be to make the caches even harder to find. Replace a few with a difficulty of 5 Nano's, at least the people who have found them before will come back to look for them again possibly.
If you do go with the game camera, try putting it in the parking area so he is not in the "looking" mode and spot your camera. You also might get a License Plate and I'm sure we could figure out who it is . If you go the game camera route, make sure you have one that is an infrared flash or turn the flash off so as not to alert the perp.
I just thought of this one, set up a new cache and just pay some local kids some Mt. Dew, 500 paintballs, and some sandwiches to sit and wait for whomever actually takes the cache without the intent on coming back.