Do your usual stuff, if a person that looks dodgy starts walking towards you, look away and ride off, now if you do see a group of lads that look like they would nick your bike, do ride away and go back there a bit later, that won't hurt will it? Now if anyone comes over to pinch your bike and you do not have time to get away, defend yourself, but do not leave your bike, if you know your gonna get beaten up, just lay on the floor with your arm around your bike frame, and do not let go!