I typically wear steel toed shoes, so I would have booted that bastard square if the face. Hopefully I'd break a few teeth and or bones, but dogs are pretty damn tough. However the force of a steel plate smashing their face with the force of a soccer kick will probably make the dog rethink it's actions.
I don't think I'd resort to pulling out a knife or anything unless the thing is going crazy and starts pentrating skin b/c things can get really tricky (with the law and stuff )when a weapon is involved. With steel boots though, nobody knows the difference b/c they look like business shoes.
I'd probably call Animal Control as well b/c I have small kids around. I'd want it documented that the dog attacked me viciously.