Things to keep in mind about dogs:

1. They are a little stronger than us, pound for pound.

2. The end with the teeth can do a lot of damage to flesh and bone, especially with breeds with a triangular shaped jaw with strong muscle attachments. (Pit Bull Terriers get this from the terrier part; all terriers have strong bites out of proportion to their size.) Keep in mind that if you present a dog your hand wrapped in a jacket or shirt you are still very likely to have blood drawn and have serious damage to bones, nerves and tendons. I've seen a small fifty to fifty-five pound Malanois female (lol, it censored the female dog word) bite completely through a police training sleeve and bloody the volunteer during training. Your shirt and jacket aren't nearly that strong, and that dog didn't have a particularly strong bite.

3. They lead with their face. Probably not the advantage you'd think, since in many breeds, that means the head/face are pretty well protected. Also, see, number 2 above. Teeth hurt. However, this also means when you're dealing with just one dog, a longish stick, like a hiking staff, can be very effective. Rather than swinging the stick, particularly if you're untrained in using long sticks as weapons, use it in a spear-like manner (without leaning into it and losing your balance) to hold the dog at bay. Getting your back to something will help prevent the dog from circling. Aiming that little rubber foot for its mouth is a plus if you can jam it in its mouth forcibly. You don't want to get into a tug-o-war, though, so present point first.

4. They take down their prey like most predators, with their body weight. Look up some videos of police dog training on Youtube. You'll notice the same takedown technique on all of them: Grab an extremity then swing the whole body on a pivot and whip the victim to the ground. Un-trained dogs intent on murder will also do this to get you down to their level. Dogs less intent on murder may go for other body parts, so protect all your dangly bits.

5. Dogs have four feet. This is pretty self evident. It's also their base of power for torquing their bodies to inflict more damage with their teeth. If you can take their legs out of the equation, you can reduce the damage they inflict. MP dog handlers with over aggressive dogs frequently just picked the dogs up off the ground and slammed them into their van before loading them up. Yeah, these guys were poor handlers in my opinion, but it's good to remember that humans have the height and mass advantage and if a dog can be picked up off its feet or be wrapped up if wrestling with it, it can be deprived of a significant portion of its ability to do damage.

6. Dogs are tough. Physically and mentally. No offense intended to those advocating .22s, but if the dog can be dissuaded by a .22, then it probably wasn't a valid threat to begin with. You should generally make ammunition choices for stopping a dog in the same light you would for facing a large, drug-crazed human male. Only a CNS shot will immediately break off an attack. If you're not the one being attacked, you can probably easily close to point blank range and finish the dog. If you're on the receiving end of the attack, good luck with that. Knives are generally worse than a gun.

7. Dogs have sensitive noses. Pepper spray can be effective, especially if the dog hasn't committed to the attack yet. They're probably the best deterrent, provided prevailing winds permit their safe use. They can be less than effective at causing a dog to break off an attack.

8. Dogs have pretty decently-sized brains. Blunt force trauma to the head can rattle their cages, and backed by enough strength can outright kill a dog on the charge. I know of at least one police dog killed by a construction worker with a length of heavy PVC pipe. The guy was exceptionally strong.

9. Dogs can't wrestle for beans. Their legs are inflexible. If you get taken down, try to wrap its rear legs with yours and control its head. Flip on your back and lock it down. Now that you've got it, don't ask me what to do with it. You might try a carotid or tracheal choke on it, but depending on the breed and the strength of its neck, that may be pointless.

10. Dogs in packs are exceedingly dangerous. Even a few neighborhood dogs who are roaming around unattended can be dangerous, when pack instinct sets in. If you get chosen as prey for a pack of dogs, get your back to something, and hope you have some means of keeping them off you.

Given all of the above, I'd suggest the following:

1. Pepper spray.
2. If appropriate, a hiking staff. Remember, poke, don't swing it.
3. If you're carrying a firearm, it should be the same one you'd use for defense against humans.
4. Don't run.
5. If taken by surprise, wrap the dog up and control at least two of its legs (rear) and its head.
6. Expect to get bitten, and expect it to hurt. Take control of the dog anyway. Only the largest breeds stand a chance to take a healthy adult male in a wrestling contest. You can't really train for this one. It's like telling someone to mentally prepare to be cut if they get in a knife fight. Prior experience handling things that bite or being subjected to intense pain in difficult situations helps... but do you really want to get that kind of experience on purpose?