At one of the ramps I used to use in NC they would drill a hole in the corner of your gas tank and drain it. That is an expensive fix. Locking gas cap won't stop a determined thief but it may get him to ignore yours and try one without it. Too bad for the next guy . Some friends of mine hid in the woods at that same ramp and caught three young boys tapping the tanks at night. After that it stopped. Not sure what happened to the boys.