I've done pillars in the middle of the tank for the Blue World 180.
In my previous 120g, I have rock piled up and it caused a nitrate sink., even though it was just rock work against the short wall of a peninsula setup.
I need more rock to mount corals to, so I was thinking of adding rock walls on either side of the center overflow of the 180. I would create the walls like I did with the pillars, mounting the rock together outside of the aquarium with epoxy. With such a a small footprint that would go in the sand, I dont think alot of detritus will build up, although when constructing the walls, I will try to provide some space behind the rock for water to flow.
I remember when Jason Fox was talking about his 700, he said he left room behind the rock and has a powerhead the blows behind the rock work.
I think building rock from teh back wall towards the front like alot of tanks have is beneficial for coral lighting and minimal shading as well as getting flow to blow "across the reef".
I'd be interested in seeing more back to front aquascapes like Jason Fox and Sanjay have. I asked jason if he had any pictures of his rockwork before mounting coral and he did not.