Declawing cuts an entire knuckle off, and usually leads to aggression, arthritis, chronic pain, and litterbox problems (which I think is MUCH worse than clawing furniture). Also, if it does somehow get outside, it will have no way to defend itself.
Use claw caps! They are little silicone covers that go over their claws. They work great, last about a month, and you can get them for a few dollars on Amazon (much cheaper than declawing!)
Also, get some scratching posts and put catnip on them (my cats love the cardboard ones). Sometimes simply giving them something they're allowed to scratch solves the problem!