I had some teammates trying to do this glitch before I even knew how. So I just camped on the spot where you do it, effectively blocking them, they kept trying to go under, were cussing and swearing at me, they wouldn't give up.
Another way to block might be to drive a tank over it.
They can patch this very easily, even after they release the game. Most games now make the floor of the "box" kill you when you touch it, I'm sure they are going to do that to all maps now. Getting on top of buildings is one thing, but under the map gives the opponent no chance and is lame.