I don't know if this will help, but my parents were the same way, they got one dog and a while later got another and for years they were fin. Minor spats here and there, but about a year ago it started to get really bad, they were fightening all the time and really fightening. There would be cuts on the and blood on the floor. They are both females and spaded, but they just fought so much because whoever didnt start it had to go back at the other one. needless to say the both have to seperated now .