There are a few tricks out thier that can work we have a lot of cats and have learned a few tricks,here they are....
1. Take duct tape and tape it so that the sticky side faces out, cats hate being stuck.
2. There is a spray at wal- mart in the pet section, to "keep cats away" there is a little bit of a funny smell and you have to spray it everyday on the spot you don't want them to go/scratch.If you use this in conjuction with the spary bottle
he will start to associate it with the squirting of the water.
Those really are the only 2 things that work well, beyond that some cats are just way to stubborn and will do what they want anyways, there is always declawing, but I find that cruel especialy if there is any chance your cat can go outside, they need there claws for defense.