First and foremost, please don't have it declawed. This is extremely painful to a cat. Imagine what it would feel like to have all your fingernails removed. My daughter Melody told me that people would bring their cats into her vets office to be declawed and not even want to pay for pain medication for them. That seems pretty cruel.
There are plenty of scratching posts for sale and you can even make one yourself and it's a much better alternative to declawing. Here is the technique we use. First, provide one or more scratching posts for them to use. Place them at or near the area they are already using to scratch. Take a small amount of catnip and sprinkle all over the post. Bring your cat over to the post and, holding its paws, make the scratching motion on the scratching posts while telling the cat how good he is. Every time you see them using the post correctly, praise them.
Now, what to do when they DON'T follow the rules. Invest in a small spray bottle and fill it with water. When the cat scratches anywhere else but the post, squirt it and tell it "no" or "bad." Then, take the cat over to the post and make the scratching motions with it's paws again while praising it. It won't take long for them to get the idea if you are consistent.
That's all there is to it. Let me know if that works for you.