What are some of the best ways to deter a cat from annoying habits? See additional info?

I have a 3 year old Manx cat who has a horrible habit of scratching at my bedroom door multiple times throughout the night. I sometimes end up getting up 6-10 times during the night to shoo him away from my door. My bedroom is upstairs and I put a baby gate at the bottom of the stairs to try and stop him but he jumps over it. I've tried leaving my door open but then he comes in and roams around and meows and keeps me awake that way. I have tried locking him in a pet crate at night and he ends up having accidents in his crate and causing a large mess. I love that cat but if I can't break this habit I'm afraid I'll have to get rid of him. Serious and humane ideas and suggestions only please :0