Thane wrote:My first impulse for that situation would be a metal bat or a tire tool, not a gun. A club of some sort.
I chased a rottweiler out of my yard once with a length of metal pipe. It proved very effective.
What would prove even more effective, however, would be a declaration to the negligent neighbors along the lines of:
"Your dog is being a public nuisance and a potential threat. If I catch him in my yard one more time, he's going to the pound. If I catch him attacking my cats one more time, I WILL kill him to protect my own property."
After I ran that one aggressive rottweiler out, that's what I told his owners. He was never allowed to run around unsupervised after that.
Some dogs would react the opposite way to this and attack you. I take it you don't have a fence, if you did you could trap it and then call the AC or police. I would call both each time the dog is in your back yard or aggressive.