^ As a dog-lover, my only answer to that is that people really should be better dog-owners. If something that horrible has to come to pass, the dog-owner really has no-one to blame but him/herself.
For me, the problem of shooting a dog is just how fast the sucker will be, and the angle of attack. If the dog is attacking either my dog or a companion, this becomes even more problematic.
Questions for the group: When was the last time you engaged moving targets? When was the last time you trained contact shots? Contact shots with our hands placed on the target?
Backdrop issues will also definitely need to be considered.
FWIW, I have not felt undergunned against dogs - but even our rather urban neighborhood ("inner ring" commuter suburb of Cleveland) still sees the occasional deer. My dog and I rounded the corner one night to come rather uncomfortably close to a large buck.....
Luckily, my dog is quite mild-mannered and controllable - so we elected to back away nice and calmly.