I would probably rent a friend's big dog for a week or so.

Use a "dog anchor", which is a big screw that screws into the ground to keep the dog in your yard, but on a leash long enough that he can wander wherever he/she wants, including to the back door. That will keep your cat inside and the raccoon outside.

Once the raccoon realizes that the cat's food and water is now protected by a big dog, he'll look for an easier meal somewhere else, and that shouldn't take longer than a week or so.

Feed the dog hamburger, and you'll both be happy with the arrangement.