"my Size 11 works quite well."
W.E.G., I'm not trying to argue much with you, here. I can agree that most of the dogs who are threatening and aggressive are not likely to do much - if any - harm.
However, I am a Vietnam combat vet and the largest non-surgical scars on my body were put there by dogs whose owners said they were friendly.
In my experience, a dog that is sick or one that has been trained or encouraged to be aggressive will attack attack attack until what it perceives as the threat - you - has departed.
I have even been bitten AFTER the owner ran up and dragged the dog away from me but didn't keep solid control. In one case recently, I started walking away from the lunging and ferociously-barking dog and its owner, constantly looking back. The dog had not stopped looking at me and was pulling hard at the leash. I was a good 15 meters away when I heard rapid running and turned around just as the dog bit the back of my leg.
I kicked at it with my size 10.5's but it was much too quick for me to hit it. The owner ran up, screaming at the dog, which ignored him. (Check with Caesar Milan as to why.) I had a Kimber Pepper Blaster II, which I had drawn and was pointing at the dog. I screamed at the owner that if he did not immediately control his dog I would use the spray, and then my phone to call 9-1-1 to file charges.
One of our sons is military and lives just off the base where he flies. He runs, among other things, to stay in shape, and feels dogs are the biggest threat to him. He said @^&% the pepper spray and carries a Ruger LCP or similar. He says the dogs are big and he wants them dead right there.
I'm at the age, with accompanying physical condition, that running is not an option and kicking, however ineffective, is worthless, never mind hard to do. I'll still go for the pepper spray first, but the dog gets only one chance to react, and then I'll shoot it with my firearm.
Finding people who have actually used pepper spray on dogs is harder than I would have thought, so my sample is small, but I have yet to find one who said a solid hit with pepper spray was not effective.