There is a cement that is used in the Wakiki Aquarium (spelling), I think its called Vertical Thorite or something. I used it in my tank to get some crazy aquascaping angles and such. Well worth it, IMO, you have to order it from Cali or something. But it allows you to make cool structures and defy gravity with the rock, so you can have more than the sloping rock wall. I used it to keep the whole back of my tank open and the rock off the glass so that flow can get back there and I can clean it if needed. Biff will be able to see what I am talking about when she comes over on Sunday. I can get you more info if you are interested, it is a good idea if you are planing on keeping the tank in the same spot for a while.