Some cats are horizontal scratchers and some are vertical. The reason cats will choose a sofa over a scratch post is the presented post was neither tall enough nor sturdy enough. If it wobbles at all kitty will forsake for the more steady, unmoving couch. The best scratch posts are not posts at all but items known as "cat trees" or "cat furniture". They usually have a very large base (at least 36" square) and the post portion should be no less than 30" tall, preferably taller. A good cat scraching tree is usually not small and usually runs around $100 or so. You can probably make one cheaper. Sorry to hijack the thread, just wanted to shed a bit of light as to why most cats will choose the sofa over that crummy little post you bought at petsmart or wallyworld. There is loads of info on the web.