Spray bottle, loud hand clap accompanied by a NO NO hollered his way, can full of small rocks to shake at his rear end, toss the shower curtain over the railing.....he's a kitten, kittens do this sort of stuff...just like puppies piddle on your rug sometimes...it's part of them being babies. I had a stubborn neutered tom that would only mind you if you imitated a cat hiss at him...hey whatever works.

Cat love to climb so maybe you could make him a multi-level cat climber out of some old carpet scraps, wood and tubes. Scent it with cat nip.