Cats NEED to scratch, it is part of being a cat. So you won't be able to stop the scratching. What you do is re-direct it to a proper place, like the scratching post.

Rub some catnip on the post to entice kitty to use that. And praise him any time you notice him using it. "Good BOY, Potter!"

Normally, I put double sided sticky tape on the furnitutre where they have been scratching, to get them to stop using that spot. Last time, I couldn't find the tape so I went into a craft store and bought mounting tape. Works just as well. But the carpet stairs, um, I would be sure to get my shoe stuck!

Catnapper is right about HOW they scratch. Sparkle likes to stretch up to her full height. The top edges of the sofa and upholstered chair used to take a beating. I bought a tall cat tree, and she uses that now. Kept the tape on the sofa and chair for about 3 weeks while she switched over. It has been 3 years now, she is using the tree only.

When they scratch, they are depositing scent from the glands in their front paws. Declawing doesn't help, because the scent glands are still present, and they still deposit the scent, making the same motions. You may need to clean the area where he WAS scratching, because he will want to redeposit his scent where he was before.

Good luck, let us know how it goes!