I don't ride where I must leave my bike unattended. But if you do, here's something that might work for you. If your bike has quick release wheels, loosen the quick disconnect when you leave it. Chances are, a thief won't check it and will wreck trying to ride it away, possibly leaving the bike at that point. The bike might get scratched, but it might allow you to keep it. Of course, don't forget to tighten the quick release when you go back to ride it!! If they're stealing it and throwing it into a vehicle, this won't stop them, of course.