Well I suppose I could give a royal a shot, make its cave entirely stone, and then just keep some "scrap wood" around the entrance and exit at all times and hope for the best, maybe if he has easy access wood and doesn't need to go through any java moss, he will just be lazy... worst comes to worst and I can either put him in a different tank, or take him back to my LFS if he's just wrecking the tank... severums are notorious for destroying plants, but I have all of mine in planted tanks and they don't bother them because I purposely overfeed them, maybe that'll work for the Royal. I'm 28 and medically retired, so doing extra tank maintenance isn't a huge issue, I've got the time lol