Well, I wouldn't do that either but if the dog is approaching and won't back off after verbal commands to do so then you are likely to get your dog bitten if you don't stop it in some way. Some dogs are very dominat and that can be bad for you and your puppy and like he said if the puppy is attacked you most often have to live with a dog that is dog aggressive the rest of it's life. Maybe the pepper spray would work better?
Be very careful with the sprays. A forum member on the shepherd forums used it once to keep a stray dog away and with the wind and everything it backfired into her own dogs face. The dog was scared to death of going for a walk for quite some time.
I've had stray dogs come up to me around this area while walking the poodles. I was about ready to beat some black lab..picked up a huge stick and everything and raised it up..he kept barking/growling and then charging the poodles but stopping about 1 ft away..
I picked the stick up ready to hit him with it and his entire expression changed and he started jumping up and down wagging his tail..so i threw the stick and he brought the damn thing back.