Well I just completed my scape today in my 200g DD. I used approximately 160lbs of Marco rock. I wanted a canyon type scape with open swim areas and plenty of places to put all of the corals. This will be a true mixed reef tank leaning towards SPS.
My buddy and I did this in a few hours without using any mortar, rods, PVC, etc. Everything is stable without those things.
Without further ado...