Why don't you get a hand-held stun gun? I have 3 of them (different sizes and strengths) that I bought in the states for protection from people and dogs when I walk on the beach. They are inexpensive, work well, and don't kill anyone/anything.
I am not a bleeding-heart liberal that would let some crazy dog put me in a position where I am a prisoner to it's bad behavior. One or two blasts should teach it some manners.