Carolyn
A small Lab mix, very timid looking -- not much protection.
I have a pint-sized Lab (43 pounds) who is ordinarily quite affable but a tiger if she perceives me as threatened. She has faced down a loose pit bull for me - Mr. Pit didn't like what he saw and turned tail.
But as I said when I was chatting with one of the police officers who does security at our church, I place my trust in the dependable products of the Colt Firearms Manufacturing Company. Of course, the biggest cannon in the world does you no good if somebody jumps you from behind with a police baton and stuns you with a blow to the back of the head. You may fight, but you've already lost.
A couple of buddies AND a good sidearm AND a good dog. Cover your bets.