They need to be trained as well. But I still wouldn't discount taking out more personal liability insurance, it's a letigious society out there, especially if someone gets bitten or mauled by a dog. They can go into the thousands in cases like that. Of course it is always best to err on the side of caution when rasing any dominant breed of dog. It is also true ANY dog can react badly if they for whatever reason determine the action is warranted.
Dominant breeds are especially prone to protecting their environment.
That said I tend to think as Brown does in that your dogs are simply establishing their pecking order. Some dogs will work this out and everyone ends up happy. Pairing some dominant breeds can often lead to unending battles only solved by parting them permanently. In my experiences most altercations are short bursts solved by the dogs themselves. The last pair I had unfortunately could not work this out.