A few years ago, we had three Pitbulls in a livestock pen on a killing spree. I killed all three with a S&W Mod. 36 loaded with 125 gr. Silvertips. One shot each.
Last year, my family and I were out walking the block (1.1 miles) in our rural neighborhood. At one house, a pit bull and a blue heeler came out and tried to attack our dog (Black Mouth Cur) while he was on a leash. I smacked the Pit in the face with the walking stick I carried, and he took off running with the other dog kiyi-ing right along behind them. The bonehead owner just stood there watching the whole time saying/doing nothing.
To hit a dog and keep him from dodging the blow, swing in a horizontal manner once he is close or charging. He can't avoid the impact as easily.
My sister and neice had the same problem in their neighborhood. I gave them some polished walking staffs, and they seem to do the trick, as the dogs stay away now.