Jump forward a few yrs. Approx 180 pounds of granite boulders, just like in the lake, with natural sand, just like in the lake. Those rocks were smooth bottomed, and placed directly on the glass, with sand added after. I never had a rock shift using this method. The look of common LFS rock (lava, rainbow, etc) never appealed to me, anymore than brightly colored gravel did.
Great looking fish and tank set-up aside Neil, that's a lovely cabinet & canopy -- really hard to find anything like that here (and what few I've seen at one Chatuchak shop cost an arm and a leg compared to a regular simple metal stand which is most common here).