I've got a bit of a problem with Tom at the moment. Given an opportunity to run off he will. He thinks it's all a big game and just goes running off giggling in the opposite direction if I call him over. Most of the time it's absolutely fine, but if we're outside it's not good. He has a bit of a habit of running around the side of next door or making a sprint down the drive. I'm a bit worried that one day he'll get hurt because I'll call him and he'll run into the path of a car or something. Any advice?