I'm not sure what you call it, but I love the "levels" or "shelves" some of you guys have in your scapes. How do you do that? Are you just building up with gravel and framing with rocks or is there some kind of armature underneath? Also can you do that with undergravel filtration?
Several ways, but the most stable method I have found is to use rocks and expanding foam filler. There is a black type that is sold for water falls that works great in aquariums. The yellow-tan construction stuff is also aquarium safe (once it has set up) and may blend better with some rocks and substrates. It can be sort of bright, though.