I have my rock leaning on the back glass in sections of my tanks. I leave the sides clear though for cleaning. Just make sure the rock is secure so it doesnt crash against the glass or shift and break it.
__________________ 180g- Mostly BIG fish and some coral. ~80g Nuvo- My coral tank with "happy fish"~ 90g- FOWLR Not the not happy type of fish~ 125g- Freshwater Malawi Cichlids ~10g- Nuvo- The refugees from the Ich of '18
Looks good if u spray paint the back blue or black u will not see all that plumbing !! I prefer black fish and corals look great against it !! Leave room on the sides so u can clean the glass just enough for a mag scraper is fine if not its a pain