My dad used a bow and blunt tipped arrows to discourage dogs. When he got older he used a sling shot and OO gage buckshot. I still use the sling on dogs in my yard. Out on the road I have carried the sling when I expected dog trouble.
As far as I am concerned once the dog is off its' owners land, is barking, showing its teeth and approaching me it is self-defense to nail it with a pellet. And when it comes to P.E.T.A. it meants People Eating Tasty Animals.