Gas cap Lock?

The problem i am seeing is, if you stop tthe kid from taking your gas cap he is just going to find something else to screw with that will mess with you. You need to just stand up to the kid or his dad and tell him its not cool. If someone did it to my car, maybe once and returned it right away, i may laugh aboutvit. But if it were a persistant thing id tell him " look the next time you do it and i catch you I'm going to slap a 9/16 wrench acrossed your knuckles and when you then try to take it again and your hands to crippled to do so, then maybe you will get the hint." Don't play the game, the more of a pushover you are then the worse it will get.