i have a 7 year old neutered amle wolfhound mastiff x, he has lived happily with our cairn terrier who is a spayed 6 year old girl, he recently started to act aggresivly towards her, and today he has attacked her, causing some nasty injuries, according to the vet almost fatal!, i love both my dogs and am distraught at the possible options, i also have 2 small children and have to considder their saftey too. anyone please help