Just got a new room mate who has a juvenile unspayed female cat.  The first
encounter with one of my two neutered male cats resulted in a nasty fight.
After separating the two into different rooms, my big guy was one big ball
of fur with every hair standing on end.  He welcomed my affection but really
wanted back out of the room for another go with the little female.  He made
repeated efforts to open the door but would obey my command to "come back
over here" when I would scold him.  (He is one of the few cats I've seen
that actually obeys instead of flipping me the bird when I tell him to "come
here" or "go outside".)
I have another neutered male but so far he has avoided contact with the
"invader".
My question is how to prevent another battle.  This wasn't just a get to
know you spat.  It was a biting, hair flying death match.  My male seems to
be defending me and his home.  Cat anyone advise on how to negotiate a cease
fire treaty?  I don't need the cats to love each other but I don't want the
little female to get hurt or worse.