I keep 4" diameter curved pipe couplings in the tank for my 22-24" fire eels, which they love to 'snooze' in. My 17" giraffe cat, Bernard, loves to redecorate, and uses his nose as a wedge and completely flip over whatever he pleases. This sometimes includes those large pipes containing a fire eel who ends up going for a ride, getting flipped onto his back (these guys aren't so agile on uprighting themselves when they can't straighten out), and facing the opposite direction. .
With my 25" and 17" TSNs, 23" RTCxTSN, 17" giraffe cat, and 19" and 22" niger catfish, I dont bother actually decorating my tank. I throw driftwood in and assume it to be play toys and territories to be built. I thought about polishing out the scratches on my 'new' 600 acrylic tank, but thought better of it when I considered the fact the my bulldozers will just end up throwing the driftwood into it and scratching it up.