I had a male last year that wouldn't lock (it was his first time lol), so I put him in the tub with his lady friend, and a third (also clueless) normal male in with them. I waited for about ten minutes (***waiting in this case means sitting on the floor and watching like a hawk to make sure the normal male didn't do anything he wasn't supposed to***) and then took the normal male out again. Jealousy motivated that male better than three months of trying (and using other sheds, plugs etc) and they were locked within two hours. Might be worth a try if nothing else is motivating him.