Sucks to have to deal with fighting dogs.
But I will say that I don’t think it’s as unusual as it might feel?
Years ago I had 3 dogs - an old husky female (alpha), a male Bernese, and a male malamute/shepherd/wolf mix (he was a drop off at a hardware store that we later tracked back to some backyard yahoo trying to do hybrids -sigh-). When the female husky was alive, there was peace all of the time. She was a good alpha, and though she’d occasionally go after one of the others, the second they backed down she let it go.
She died and the berner died, and we got another male berner. He was raised by the malamute mutt, who did his best to become the new alpha. But he clearly never really learned how to do it, and he would go after the berner like the old husky had, but he absolutely would not stop. It took my husband picking him up by his butt and shoulder skin and removing him from the situation. If you pulled away the berner, the malamute would stay on him, and if you just pulled away the malamute it would keep going. The couple of times I was home when it happened, I tried prying them apart with rakes and couldn’t do it.
Long story short, once every 6 months or so, they would get into that awful fight, and fortunately my husband was usually around to deal with it. The couple of times he wasn’t I was eventually able to get them apart. They did cause each other to bleed, but via small puncture/teeth marks…a lot less damage than they were capable of.
I always assumed the malamute took issue with the berner and sensed that he wasn’t healthy. And the attacks escalated a bit as the berner approached his 8th birthday and then just died in his kennel one night.
Cue another couple of dogs. The malamute raised our corgi and our next berner (female this time). And he did the same thing a couple of times to the berner, but not with as much ferocity, and the berner always backed down immediately (unlike the boys). The malamute passed away at 13. And lo and behold, once he was gone, the corgi started the attacks on the berner.
It’s not a very high risk situation - the berner literally stands there confused when it happens. But it’s still something where we generally intervene and pull the corgi away. And it’s probably the same frequency - once every 6 months or so. They get along great all of the time otherwise.
My point is just that I don’t think it’s that unusual.
But I too learned that you don’t ever intervene with your hands! I got bit by my first berner (who would have died for me!), by inserting myself in the middle of it. Hence the husband picking up the malamute and/or rakes.
Seems like other people have good advice. But I haven’t ever found a way to make the behavior non existent!