My mare is in with a gelding and they actually get on really well, better than i thought! when my mare comes in season (which she is in now) she is sometime abit mardy with him, but you know us giurls!
What we use is two big tractor tires, one on top of the other, place a wood board between them so the hay doesn't go to the floor.
And then just fill with hay and they will munch quite happily!
:D