...another method besides the two listed above, this is my personal preference actually....take some rubble rock and fill the bottom of a small plastic cup or glass/shotglass/etc then place coral (xenia, kenya, mushrooms, zoos, leathers, etc) then take a small section of onion bagging and place over the top of cup or whatever and rubberband it down....it allows the corals to naturally attach onto a rock in low flow while not blocking any lighting