Clip your nails man. You know what they say about an ounce of prevention.
Seriously though, on a previous car I put some nicks into the leather on my steering wheel with my finger nails. It really p*ssed me off too, because they some of them were more like deep cuts than nicks. Now I'm almost obsessive-compulsive about keeping my nails trimmed. It's funny how cars can make one change his habits!