I was chased by two dogs at once while going probably in the high teens 18? don't know exactly. There were tall fences on each side of the road so the dogs had to come from behind. While pedaling I turned around for a second and with my water bottle sprayed and moved the spray back and forth in the area of their faces. I hit both of them in the eyes somehow. They stopped. It has never happened again, and it was years ago. Also, very important, it was a rural road with no traffic, and excellent visibility forward, and to the rear. Maybe I weaved around on the road, I don't remember. I have no idea if there was any wind, I was concentrating on spraying backwards and riding.
I was just as amazed as anyone else by the fact that I hit them both in the face while riding. It was not difficult. If the wind was right I could easily do the same with pepper spray. Actually the spray I have is a foam that is not effected by wind as much. It also has a wider spray pattern, giving much easier target acquisition than the water bottle stream. I have practiced this to get it right. You really need to try it before doing it on the bike. I would still use my water bottles first.
I am used to doing things while riding. I take almost all of my photos while riding. Often of other riders near me, including behind me. Not when going fast.
With low traffic it was easy. In heavy traffic I would not be able to turn around. I think it would be almost impossible to do this in traffic.
The busy streets where I live have no dogs that I know of. Hopefully the owners are worried that the dogs would be hit by a car and keep them in the yard.