I have found that for most pet dogs a loud, low, NO stops them. I use it right away, all the time. "Go home" works a lot of the time too. I really yell as loud as I can. I combine that with trying to outrun them if possible and a water squirt if I have enough time and can think of doing it. But the NO should always be yelled. If nothing else it might get the attention of the owner if you yell it right when they start out of their yard.
I've also swung my full-sized frame pump, back in the day I carried one. Again, like the water bottle, it requires that you're at a pace that you can take a hand off the bars to grab it w/o dropping it or crashing. If I'm in the sprint mode, that and yelling are the only weapons I have, I can't grab either bottle or pump at that point.
If I had a chronic problem with a certain dog at a certain location, I'd set up to safely (for me) spray them with pepper spray, stop the bike and do it.