Strays are a bit of an issue in my area as well, sometimes pits, sometimes other breeds.
When I walk either solo or with a dog I carry a walking stick that used to be a rudder handle - very sturdy and good reach - as I have for years, long before i had a carry permit. I still carry my ccw with me now, but for both 2-legged & 4-legged threats (maybe less so for 2-legged) I would respond first with the stick.
For most dogs, a simple poke has been enough to get them to move off. In a few cases, a solid whack on the butt was called for - but have not yet felt the need to put one down.
In the case of an obviously viscous and dangerous animal with intent to harm - I would not hesitate to react other weapons at my disposal.
"The best diplomat I know is a fully charged phaser bank" - Montgomery Scott