There is a product sold called Soft Paws as well as some knock-off variants I'm sure. They are basically little caps that glue onto the cat's claws. They still allow the cat the stretch the claws and act like they are scratching and so forth, but the caps themselves are blunt -- so no furniture damage. The cat won't even know they are there.
They are digestable if accidentally eaten (rare) and non-toxic. They fall off naturally as the nail grows, so would need to be replaced every couple months or so. You can apply them yourself.
A great alternative to declawing, drugs, sprays, vigilent training.