A common concern of cat owners is that their cats will damage furniture, carpet, or draperies with their claws. Since cats have an innate need to exercise and use their claws by scratching, it can be difficult to train a cat to not scratch vulnerable materials. A number of chemical deterrents and other options are available to discourage cats from approaching your furniture in the first place.
If you don't mind spraying your furniture and curtains with a liquid solution, several homemade compounds that can be used to deter cats from getting near enough to start scratching. Furniture legs can often be protected by citrus-like wood polish or some other heavily perfumed wax. Cats dislike strong odors will usually not risk transferring some of the odor onto themselves, which can keep them from scratching at furniture legs.
The same rules apply to fabric. Strong-smelling or particularly reactive scents can make furniture too unpleasant for a cat to jump on. Depending on what solution you want to use, there are several options. Try using a spray-on mixture of water and different kinds of pepper, especially spicy peppers like cayenne, which you can use to coat your fabric, as long as you choose an out-of-the-way test area first to make sure the pepper will not stain the fabric itself. If you don't want to use pepper sprays on your furniture, you may want to try a better-smelling option, such as orange oil (try about 20 drops to each quart of water) or eucalyptus oil, which have similar reactive odors.
If you cannot keep a cat from scratching by using scent, there are more drastic options. Coating furniture arms with double-sided tape that will catch at the cat can be an effective deterrent too, although it may make your furniture difficult for you to enjoy, too. Options like covering furniture with plastic can also prove annoying, especially from an aesthetic perspective. Try to position a scratching post for your cat near the furniture, and try to train the cat to use the post instead of the furniture--having another option that is allowed may provide all the incentive your cat needs, especially when used in combination with one of the odor-based deterrents. Aluminum foil has also proven effective, at least in the short term.