I came up with a better idea ... I hope. Instead of moving the plate, again, and just have him move right back I got some small pieces of rock and made a small wall between the 2 corals. That should keep him from getting anywhere near the other plate and the "bridge" is large enough that he won't be able to reach over it & touch the other coral even if he moves right up against it - I hope. We'll see when I come home this afternoon when he is fully extended how clever I really am.