This tip is a really cheap way to win Arena challenges.(Hey, a win is a win!) First, go to the old abandoned highway. You will start at the top of the talles building there near the corner of the fighting area. Turn around and carefully move to the corner. Once in the corner(the closer you are to the edge the better), turn around and face the enemy and shoot away at them. More likely than not, they'll end up outside of the combat area! You WIN! cheap but effective.