“self defence” usually only works if you can show that all other options, like retreat, have already been exhausted. which in this case is having an impenetrable defence. And besides, I do not think self defence should be applied to the protection of mere property anyway. (Did you know that under German traffic rules, you are required to run over small animals if they are on the road? They are not an important reason enough to endanger traffic by braking or swiveling.)