To be sure, of course I would shoot a dog in self defense or in defense of another person if it was attacking. I wouldn't like it, but I'd do it. However, if I knew beforehand that a particular dog was a problem, I'd call animal control/police/authorities. I wouldn't wait for the dumb**** owner to let his dog free so I could shoot it.
Unfortunately, if the dog was captured by animal control, my best guess is that it would end up being euthanized anyway considering its aggressiveness.