Some kitties have a hard time using a scratching post for the first time.One thing I've noticed is that a lot of scratching posts sold in stores are covered with a shaggy carpet. If I were a cat, I'd hate to use those -- my claws would get caught in the shag and be hard to pull loose.
When we made out own cat tree, we approached it from a cat's point of view. That is, start with the concept of scratching -- what is the purpose?? Well, cat claws periodically shed their outer surface, taking with it the sharp tip of the claw. What this does is replace the possibly worn tip with a new, sharp tip. Cats are genetically programmed to find a rough surface, like a tree or rock, and work their claws over it to help shed the old surfaces of the claws.
So, applying this thinking to a scratching post, you want to simulate what cats would be looking for in nature to serve the claw shedding purpose. That would be a hard and rough surface. Definitely not a soft, fluffy shag carpet. After all, which part of the furniture do cats tend to go after -- the hard corner of the couch, where the wood is right under the surface of the cover fabric and where the fabric is held firmly in place by tension, so that the claws can be pulled free easily if they should catch.
Don't be fooled into thinking that just because all you ever see are the shag carpet scratching posts, that those are the ones that the cats will prefer. Just remember that the scratching posts are designed to be sold to PEOPLE, so they must appeal to the person with the credit card. You never see a person bring his cat into the pet shop and ask if his kitty can try out the scratching posts!!
When I make a scratching post, I either wrap a very short nap carpet around a 4x4 and make sure it is stapled tightly to the wood, or I get a short log and nail a piece of wood to it so it doesn't roll around when in use.
And be sure to train your kittens to use the correct scratching post as early as you can in their life. Nobody should have to put up with torn up furniture. I never did.