Purple corraline growing on the back glass for those with front viewing tanks is pretty much a standard IMO
. Rocks on the back glass too.
If I were you, I'd use the large rocks on the very bottom of the tank. Try to wedge or stack some smaller ones after those. When It gets to precarious with smaller rocks (being unstable or too loose, I'd consider doing without them and getting larger base to use instead.
From the looks of those smaller pieces, I think you've been having a real hard time using them. Maybe give'm up.