If I walked anywhere that was a remote possibility I'd walk with a hiking stick and use the stick as a defensive weapon even if I were also carrying a gun for 2 legged threats. Georgia is pretty gun friendly but even here it would be hard to justify shooting a dog.
This is an interesting proposition, and one that in which I have an actual experience.
I have a very old hickory walking stick that I've used often when walking one of my older (calmer) dogs. A couple years ago, we were charged by a large pit-mix, came out of a long driveway with a full head of steam, teeth bared, frothing at the mouth and very aggressively barking. I put the staff out in front of us (tip on the gravel shoulder, angled) while my old girl quivered in fear (she doesn't have an aggressive bone in her body). The aggressor dog litterally leapt at my stick, got the lower third in a death grip in his jaws and battled me for possession of it (he was winning). All while I was trying to maintain a two-hand grip on it while the lead's loop was in my left hand. I was struggling, and very ready to drop my stick and draw my SIG P-227 (11 rounds of Golden Saber 230 gr JHPs) when a woman came running down the drive (about thirty yards from garage to roadway) toward the road yelling, screaming and amazingly, accusing me of attacking her dog.
She stupidly came up behind her dog, attempted to grab his collar, he turned on her, snapped at her and almost bit her hand. Her teen son appeared on the scene with a leash, got the dog under control and dragged him off while he was still in a frenzy trying to slip his collar and charge back at us. Accusations from both sides ensued (I was furious that she didn't have the huge (very expensive-looking and ornate) wrought-iron gate on her driveway closed, she accused me of striking her dog. I casually moved the right side of my jacket back to reveal my badge clipped on my belt in front of my OWB Kramer holster... pulled my phone out of weakside jacket pocket and offered to call the sheriff's office watch commander if she cared to discuss things.
Apologies were then offered and accepted on both sides; she admitted she'd forgotten to shut her gate after she and her son returned home and she turned out to be a nice person (didn't hurt that she was extremely attractive), we had a good conversation about raising puppies, especially those from the more assertive large breed dogs, as well as the importance of socializing dogs at a young age with other dogs.
Until a person actually experiences this it's hard to image just how blindingly fast dogs can be, even fat dogs you think are slow.
This, and the fact that I was rather day-dreaming and enjoying an uncharacteristic sunny winter day, low situational awareness -- didn't have time to even set myself for an attack, even though the dog involved always barked aggressively at us from inside his fenced yard when we walked by (like an inmate chipping at the CO's from his door after getting celled in for lockdown).
Anyway, my point is, I wasn't even prepared to deploy my hefty stick (and I have well over thirty years of training with straight batons, collapsible batons, side-handle batons like the PR-24, riot batons but never training on how best to deploy a stick against a dog). So I learned that a large stick will only piss a really strong, aggressive dog off, and he will fight you for it.
I cannot see any reason to ever use shot-shells from a handgun against a dog. #4 shot? I can't see that being effective at all, even with a head shot.
OC? Good luck with that. Maybe if you have a few seconds of warning, but that dog will be on you before you know it, so you better have a fogger, not solid stream, and hope the wind's not blowing toward you. If you carry OC for any purpose, you absolutely must have practiced with the variety of canister sizes, propellants, activation methods, ranges, etc.
Thankfully I have fully fenced acres enough to allow them to run free every day, good for their bodies, minds, spirits.
This is the ticket. I still walk my dogs down my rural road though, mostly for my exercise to be honest, and meet all the folks who live on my dead-end road and walk their dogs too.