This actually happened to my parents older dog, Jack. He was on lead on the pavement, and a staffy rushing out of a house and locked onto his neck/shoulder area very, very suddenly. Tore his shoulder muscle and it took four people to remove the attacking staffy.
It was a trauma for all involved. Luckily, after great expense, and a lot of recovery time, Jack made a full recovery. The staffy had been stolen four years before, and abused, and was reclaimed by the original owners, with warnings and advice from the dog warden about his dog aggression since being stolen.
My advice is to practice situational awareness at all times. I'm wary of dogs I don't know now, especially in an area like where my folks live, which has...lets say... not always the most committed loving dog owners? Lots of status symbol dogs. I carefully watch dogs I don't know, put mine on lead and stay near an exit if I'm concerned, and leave if it's a dog I know isn't good with other dogs or may be aggressive.
Witnessing another dog attack in a local park, a friend of mine, thinking fast, lifted her labradoodle over a small fence that separated the childrens play area from the field the aggressor dog was charging across towards us. Genius! She thought fast, and her dog was out of danger and contained. So on walks, I keep an eye for fenced/enclosed yards where I might be able to separate my dogs from an aggressor.
Getting to know other dog walkers in your area helps too. If your dogs get along and aren't reactive of course. I've learned about some dogs to avoid through regulars on certain walks. Also heard about the update on the park attack where my friend put her labradoodle over the fence- that dog attacked another dog during that incident, which luckily wasn't too badly hurt. But the owners of that dog eventually had both their dogs seized for being out of control or something. They escaped regularly, and had attacked before.
Nettle's VoD advice also really works. I've used it, when needed, and it has worked for me. I've also been less professional and calm under pressure, and yelled at a woman to get her damn dog when her husky was far too persistent in trying to get at my two, and his hackles had gone up. Other dog walkers helped me form a body block, and she came and got her dog!
I always carry my mobile phone, charged, when on a walk. I have the vets, emergency vets number, taxi and local friends with cars numbers programmed in, in case the worst happened and I needed transport. A tennis ball thrower makes it easier to play fetch, but also works as an arm extender/blocker and potential defensive weapon. loads of treats, because treat bombs can be a great distraction while you get you the heck outta there, and use the situational awareness. A belt, scarf, or shoulder loop from a handbag or rucksack can work as an improvised collar/lead for a stray dog, or one you've separated from your own.
You can do all of those things, and the worst can happen. I'm lucky I guess that my dog survived... so it wasn't the worst thing that could happen. But it was truly awful that our sweet, innocent spaniel was badly hurt, and we couldn't prevent it. All we could do was give him the best vet treatment possible, love on him and support his recovery, and make many calls to the dog warden. A dog on dog attack with no humans hurt, in the UK, is viewed as a civil matter, rather than a criminal one.
So you do whatever you can to avoid before it reaches that point. If the worst happens, you do what you can in the moment, and you get through it.
. According to the paper the dog lives 10mins from me which is why I'm so worried and want to know what to do if this happens. He attacked a corgi and a shih tzu that both died, a Rottweiler and Golden Retriever that are seriously injured and are recovering in vet hospital.
It also depends, of course, on the size of the dogs. If they were both small I'd be more likely to risk injury for the sake of a dog than if they were large. That still doesn't mean that one should risk injury.
In your shoes, especially having seen the dog in action yourself, I would be driving a good five miles or more away for walks. Good luck, please update when you can! xx