Have LOTS and LOTS of cat furniture and make sure they know it is theirs to use. Use catnip on the cat furniture and you can get a spray to keep cats away from certain areas that you may try spraying on/around your furniture. My experience with those sprays, though, is they work FANTASTIC the first day/few hours that you spray it, but it does wear off pretty quickly (we had a very hard time keeping our cats out of the Christmas tree last year...).

We just purchased new couches and my boyfriend was very worried about the cats on it. Neither of ours are declawed... but they are VERY good about using their furniture and leaving ours alone. Also, this may or may not make a difference but I figured its worth mentioning -- my cat's furniture is in the living room, they have a scratching post and a cardboard scratching toy. I leave the cardboard scratching toy under my coffee table so it's close enough by that, if they feel the need to scratch on something, that is RIGHT THERE and they don't feel the need to scratch on our couches (at least, that's the logic I make out of it. This might be true, I don't know, but it works for us).

Good luck.