How about puttina small tracking device, like the use on vehicles, on one of the stands. The money spent to catch them will be worth it.

http://gpsinformation.net/main/vehicletrack.htm

Or camoflage some trail cameras next to your stands, and hope the tresspassers don't see them. If it were me, after the 2nd stand, I would've started some preventive action against the theives.