Unfortunately, I have experience in breaking up dog fights. I have 2 b.itches here who would kill each other if ever given the chance, or if we make a mistake.
These 2 girls lived together without incident until the younger one was bred and had a litter. She immediately took a dislike to the older one, and we were never able to get her over it. For their safety, and that of everyone else in the household, they live separated. We have a 2 barrier protocol in order if either of these girls is loose outdoors. Meaning, if one is outdoors, the other one must be behind an escape proof barrier in the house. Either crated, or in my office where we have a tall (40") very secure gate.
We also NEVER move one of these girls without visually verifying where the other one is. Since we have discussed and initiated these rules, there has not been an accident.
A serious fight between 2 large dogs is a VERY DANGEROUS OCCURENCE. I keep bear spray in case it ever happens when I am alone.