Have you tired shutting them in different room immediately after these fights and giving them both time outs? I did that with Samantha and it only took her about 3 days to learn to STOP attacking. Each time, I left her in there longer and longer and she could not stand being shut in a room. They still are not great friends now but they do tolerate each other being in the same room or walking by. I am going to have to try that with Kitty Boo now.