Scratching is a natural, necessary behavior. It sheds dead nail sheaths, stretches muscles, and marks territory visually and with scent. You cannot stop a cat from scratching, but you can redirect it.
Material and Stability
Most cats prefer sisal rope or cardboard over carpet (which looks too much like your rug). The post must be tall enough for a full stretch and sturdy enough not to wobble. If it falls over once, they may never use it again.
Location
Place the post near where they are currently scratching (e.g., the sofa corner) or near sleeping areas, as cats love to stretch and scratch upon waking.