i have a 75 gallon tank, so what i did to start is cut a piece of egg crate for the bottom then set all my base rock up, then added 1/4 tank of water, then added the sand i used 80 lbs of play sand ($8 at home depot, CLEAN WELL), then added the rest of my rock, and then filled with water the rest of the way. If you want to add more rock like i did clear the sand slowly (as to not stir up the sand) so you can see eggcrate and place rocks down then move sand around the base of the rock to fill it in. I used some slate, lannon stone and field stone only 2 pieces i got from a lfs years ago the rest i found randomly.
the cichlids dig like crazy but i havent had any issues of rocks falling ever make sure you have a good base dont put the rocks on glass eggcrate all the way