I was thinking about dog attacks too. Not necessarily due to an encounter like this, but because of my recent experience with my dogs. The other day I was playing rough with my 80+ pound Golden Doodle and he was reciprocating with equally rough play. During this time I was thinking, "I'm glad this dog likes me, because if he REALLY wanted to hurt me, it would be very difficult to stop him".
It is not just the big dogs. Another time I was trying to hold our 60 pound dog in one spot while she was being neurotic about something that scares her, and I could not do it. Even with my arms wrapped around her torso and holding on to a couple of her legs, she wore me down in a reasonably short time.
Pepper spray would work great on one of those days when you happen to be standing (or can position yourself) upwind of the dog/attacker. Then again, if you spray it and it blows back to cover you, maybe you will taste bad enough that the dog will leave you alone.
I am NOT a fan of firing a "warning shot" when it comes to humans. If you are facing a human attacker and you have been forced to draw the gun, you must proceed to fire unless the BG immediately turns and runs. However, considering a human knows what a gun is when they see it, but a dog does not, would a warning shot into soft(er) ground be enough to deter a vicious dog? Considering how hard our soil can be in the dry months, maybe you would still have to be concerned with ricochet.
Fly