My cat's have always listened to my every word. I say "don't scratch" and they stop right away
When you get a scratching post, make sure you play with the cat so it knows that scraching the post is ok. As soon as it starts scratching something it's not supposed too, grab the cat and place it on the cat post and encourage it to scratch. It sounds odd, but it works.
Don't de-claw, that's cruel IMHO.