You're all whimps and you should all HTFU.
You don't need a freakin gun to scare a dog.
Let me explain you how to handle attacking dogs:

1) turn to the dog and look him straight in the eyes. (this will make you look fearless)
2) pick up any big object, like your bike, and hold it in the air above you. (this will make you look huge)
3) start making extremely loud weird noises while moving in the direction of the dog.

Still will scare off 99.9% of all dogs. In case you happen to meet that one dog in a thousand that does not get frightened by this ... you'll simply have to let him bite you in one arm while strangling his neck and main blood vessel to the brain with the other arm. If you do it right, the dog should stop biting you after about 45 seconds.

Good luck

P.S.: I'm immune to rabies ... that helps too.