Jesus! A gun?
Pepper spray! It incapacitates the dog enough for you to get away and is harmless long term.
Let me tell you a story about my husband biking. He was close to home, but a big dog ran out towards him from someone's yard so he sprayed it with pepper spray.
The dog went yelping back towards its house, so my husband slowed down and saw the owner let it into the house. He decided to go back and tell the lady what he had done so she could know what happened and to wash the dog's eyes out.
Well, when he told the lady, she started screaming at him that he had hurt her dog and he tried to explain that the dog had come chasing after him on his bike and he was protecting himself.
Finally, he hears a man's voice scream, " What the hell, Mary!?! I told you not to let the dog get out of the damn house, again!"
When the husband came around from the backyard, my hubby said, "Look, man, your dog came after me, so I sprayed it with pepper spray. Just wanted to let you know to wash its eyes out with water."
"It's alright, dude," the guy said and continued screaming at his wife about how stupid she was to let the dog get out and what a liability that could be if that guy had got bitten and you'd better be damned glad that he only sprayed it with pepper spray, etc.
So, my husband came home, which was just around the corner and was shaken up, but he said for how well his concern over the dog was taken, next time he would just spray the dog and keep on pedaling.
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Terry, keep an eye on those bites for infection. Puncture wounds are very deep and a dog's mouth is full of bacteria.