Routinely clip your cat's claws or cap them. The only other way to stop this is to declaw them.

Here is an article written by a veterinarian about scratching.

http://www.catscratching.com/

Actually tin foil on the parts where they scratch (temporarily) should do the trick. Cats HATE tin foil and if/when they try to scratch and hit the tin foil they'll learn to stop trying. You can then remove the foil and they should leave it alone.

Also... Since I'm not a fan of declawing, I recommend a great alternative called "Soft Paws." They are awesome and cheap! Typically you can buy packs of 40 or so for $10 or less. Basically they're a plastic sheath that you fill with glue and place over your cats nail. Doesn't hurt them a bit! Of course your cat will hate it at first and try to shake them off but it's a really good alternative to surgically tearing out the nail and 1st digit of the toe.

Good luck!

Easy, there's a spray called "Bitter spray or Cat away" and that stuff works, if you want to go all natural, try lemon or lime juice, also, to encourage your cat to use the scratching post, try rubbing catnip or using a cat nip spray on the swcratching post.

if the spray or citrus on the couch juice don't work, try using a squirt bottle and spray the cat when you catch them doing it, it won't hurt them, it'll just shock them