I used to have two West Highland Terriers, who thought they were big dogs but were actually quite small. I had them out walking on leashes, and along came a Rottweiler not on leash, no owner in sight. My dogs yapped, and the Rottweiler attacked. I didn't have time to think, pulled back hard on the two leashes to pull my dogs backwards, while kicking as hard as I could at the Rottweiler, and screaming. I don't think I hurt him, but he did run away.
Good point, MesaMan, about the 'kicking through'. I did a short stint of martial arts last year, and was amazed at the difference that made.