Agree with the other gents. When using rocks, I always preferred larger granite boulders, kind of a less is more way of thinking. Taller boulders also creates line of sight breaks, and aesthetically I also liked the look. It took a while to find larger boulders with flat bottoms, but time at a local wholesale supply yard did the trick. I place them directly on to the glass, then add sand, that way no amount of digging will ever cause an issue with large boulders falling over.
The real key I think will be getting a larger group formed, one hyper Dom male tropheus is not a good thing, no matter how you scape your tank.