A colleague of mine was bothered by yobs gathering on a street behind his garden wall, playing loud music on the car stereos, revving up and ragging around. Calling the Police had failed to resolve the problem so he collected a bag of nice round pebbles from the beach, bought a catapult and set up in his front garden one night. He calculated the trajectory and began firing pebbles over the roof of the house. By pebble no 3 there was a loud revving and screeching of tyres they all shot off, never to return. Job done.