Cats and leather really do not go well together. The best tip I can advise you is to teach your cat how to use a scratching post. Keep them on both sides of the couch, and gently pick them up and put them on it if you see them trying to use your sofa.

Another thing you can do is put large throws over it. Keeping them away, might be impossible but you can teach them not to claw it. You can also buy soft paws which covers their nails:

http://www.softpaws.com/?gclid=CL7mrZGa5p4CFShSagod3k-xJw

Again, I need to stress that keeping cats from leather is like trying to keep a tiger away from a steak. It takes patience and training for both you and your pet, good luck.

You might try putting something on the chair that the cat won't like - I'm thinking of crinkly paper, nothing that will harm them but that they won't want to walk on or listen to under them.

I looked online too and something like this http://www.jumpotrainer.com/ might work but it depends on if you want to spend money or use something you already have.

This quote comes from http://www.petplace.com/cats/how-to-keep-your-cat-off-tables-and-counters/page1.aspx but is also along the lines that I am thinking of.

"Booby traps/mild punishers. Various booby traps have been invented to deter cats from counter surfing. Some of these deterrents include: putting cling film over the countertop, making a shallow tray out of aluminum foil and filling it with water, various springing devices (upside-down mousetraps or proprietary plastic jumping frogs), or attaching a black thread "trip wire" across the access to the counter and attaching it to a nearby pile of shake cans."

There is of course actually training with positive reinforcement with clicker training as well but that might take alot more time.