[spidey]

I'd never do this - same sex, similar age, both large, typically same-sex aggressive breeds...it's asking for trouble, and 6 months is plenty long enough for the Tosa to get comfortable enough to start looking for trouble with your Rottweiler (you likely haven't seen problems before now because the dogs haven't lived together for any length of time). I think this is a very dangerous idea, for dogs and people, if a fight breaks out, your dog could easily be killed and you could be seriously injured.