I bought my LR from Harbor Aquatics and followed their recommendations for supporting the rocks as shown on their website (http://www.harboraquatics.com/setup/index.html). I cut lengths of 1-1/4" PVC pipe in lengths equal to or slightly longer than the desired depth of my sand bed. The pipes rest on the bottom of the tank. I used three of them to set each rock on, with a few 1" sections here and there for smaller pieces. It was kind of a hassle and took a while to get the bottom pieces stable, it involved trial and error in placing the PVC pieces until each piece of rock was stable, and if you want to move the rock a little you have to move all 3 pieces. However it was effective at creating open space around the base of the rockwork for water flow and the structure seems quite stable. Later on when I re-did my sandbed I switched to some sections of 4" ABS to set the larger pieces on and it seemed to work better than the tripod method. All of the pieces of pipe have lots of big holes drilled in them so that water and critters can move through. The other thing you need to know if you use this or a similar method is that some sections of pipe may be visible around the base of your rockwork. You will need lots of smaller pieces of LR to place around the bottom to conceal the pipes. I did this and you can't see any of the pipes. I don't know if this is the best way to do it but it worked for me and I am satisfied with the results.
Good luck,
Robert