I build a PVC stand out of 1/2", next one 3/4" PVC, first one white, one in process black from Savko.com, drill holes through the PVC so that they take on water. Drill holes through some of the rocks and attach them to the PVC with plastic zip ties.
I am making my first attempt at ledges. I have a 1/4" nylon rod and am drilling holes in the rock, putting some aqua mend (from Home Depot) in the holes and inserting the rod in to each rock.
I probably should have got larger diameter plastic rod, someone suggested plastic coat hangers.