[spidey]

Having lived with two male dogs who hated each other (both under 60 pounds, both of normally dog-friendly breeds, neither bred for fighting or protection, so NONE of the issues you have in this case, other than same sex similar age dogs in the same house, and STILL a dangerous situation), it was stressful and regularly nerve-wracking, and the few occasions when these dogs were accidentally allowed out together resulted in trips to the vet emergency clinic.

PLEASE RETHINK THIS - you are VASTLY underestimating how dangerous a serious dog fight can be, and with these two breeds, it could easily be fatally dangerous, are you honestly prepared to take that risk? People who have never experienced a real dog fight first hand always seem to assume that those who have are overstating things, I assure you that we are not. Pretty well every time I discuss dog aggression with people who have never experienced a real dog fight, they assume that a dog fight is the loud snapping and snarling you see at the dog park, everyone has seen that, and dogs rarely get hurt in one of those, right? Right. But that's not a fight, that's an argument, the difference between one of those arguments and a fight is the difference between a lawsuit and a contract killing. The point of an argument/lawsuit, is to resolve a difference or punish a transgression, the point of a contract killing/real fight is to permanently take your enemy out of the picture. In the wild, dogs who have serious issues with each other do not live together, one will leave or be chased out, so it rarely escalates to the level of one killing the other, in a domestic situation, the tension builds, there is no resolution, and one dog will try to kill the other. Please believe me, everything might be fine, but if it is not, you do NOT want to be stuck in the middle, and keeping 2 large dogs 100% separated 100% of the time is much harder than you'd think, especially if they have a real hate for each other. Dogs can and do kill each other distressingly often, much more often than people think, and it is almost always in precisely the sort of situation you're considering having in your home: same sex, similar age dogs living in the same house.

The responsible thing to do for your friend is explain why this is a bad idea, and help him/her find alternate arrangements (perhaps with the Tosa's breeder?).