I have two Australian Cattle Dogs, both females, that hate each other. One is about a year old and the other is about three. The vicious fighting started last year. They mean business, and we have incurred several large vet bills because they tear each other up. The fights seem to be over me; when I show attention to one, the other bristles up, and then they'll just explode into a violent fight. They get along okay during the day when I'm gone, but they can't be in the house together if I am there. I have to keep one in the bedroom if both are inside. I feel like I'm walking on eggshells, waiting for a time bomb to go off. What can I do?
I could give you a long-winded, optimistic reply about how you could modify the behavior over time and get the two to peacefully coexist. Some trainers would do that. I won't. Life is too short, and no one in your household is happy right now with all this tension. For the sake of everyone, re-home one of the females in an environment that's more suited for her. (i.e., no other females, no cats, whatever...)
Your situation is not unusual. You have two strong-willed, same-breed females--tenacious "heelers," no less--and there are serious issues between the two of them. While the fights probably do start over you, the tension is always under the surface, and you're correct to liken it to a time bomb. You simply shouldn't have to tiptoe around your own home and dogs, nor should you take the chance that you can affect the behavior sufficiently to make a permanent change. Certainly there are steps you can do to postpone another violent fight, but the next one could be the worst yet, and will likely occur when you're least expecting it.
Years ago I saw two red female Dobermans, littermates, try to kill each other in my class. They blew up so unexpectedly that none of us saw it coming. The two young dogs had been sitting quietly and obediently next to each other with their owners when they suddenly exploded at each other. We managed to get them apart, but not before one had torn her sister's ear and left puncture wounds on her muzzle. The owners then told me this was an ongoing issue; the dogs had hated each other since adolescence, and their fights had resulted in numerous visits to the vet. We explored various types of behavior modification, ways to mitigate, ways to better expend the dogs' energy, ways to manage them. Yet I was pessimistic about how much success they would have. Frankly, I could see the people were not up to the task. It would have been a lot of work, with no guarantees the fights would stop.
Like your situation, each of the dogs was great without the other. Each was entitled to live a life of peace and low stress, which would not be possible if they lived together. Careful re-homing may be heartbreaking for you, but it would definitely be in the best interest of the dogs you love.