Region Trigger Help

Have a trigger question, here is my setup.
For now I need all players to be allied.

I have a square drawn which is also a region.
I need a trigger so when a peon enters he becomes the owner of that square. Then when another peon from another team enters it explodes that first peon and the new peon becomes the owner for that square. Also if that peon leaves the square it becomes fair game to anyone else.

Maybe to set a variable for each square and do checks every so often.

Thanks for any help.

Umm... how exactly do you "own" a square?

Got some help from a friend. Thanks anyways