Has the cat been checked for a medical problem such as an UTI? They will go anywhere when they have one of these cause they associate the pain with the litter box. If a medical problem is ruled out, then it is behaviorial and there is medication a vet can prescribe to help control this.

Also, we use scat mats on our furniture. This does not hurt the cat, basically startles them. It feels like a static shock. They work wonderfully. Then when we want to use the furniture we just remove the mats, and a plus, there's no hair on the furniture.