Cats will find something to scratch, whether they choose the scratching post left out for them to use or your favorite couch. By scratching furniture, your kitty is leaving a visual marking, which is a healthy, natural, and territorial behavior. Your cat wants the damage that they do to be obvious, not hidden in a dark corner where nobody will see it. If you have a scratching post hidden away, they will choose the couch as their new scratching post. The couch is always in an open area where everyone can see it making it more appealing than a hidden scratching post. Though the scratching post may be unsightly, keep it in the open if you want your kitty to use it properly.