Mine did the same, he ALWAYS took off after the runners past my house and he actually bit on but she was a friend and she knew it wasn't a real bite (he likes to hold your hand when you are walking) but he did it when we weren't home so he now at all times has to be tied up... i feel bad cuz he is a husky and loves to run but he is all the time tied up.
that is basically all you can do unless you get that underground fence like i am!