We've got the same problem with our stair carpet. When we had a carpet fitter in this week I asked him what we could do about the tufts she has pulled out, he told me to shave them off and then rub orange, lemon or any citrus peel onto the carpet as cats don't like the smell of it and will run a mile from it. He said it won't do any harm to the fabric nor discolour it - worth a try 'specially if you eat a lot of oranges and it will keep your house smelling nice into the bargain lol.