Buy a new one when they come out a year later
Not sure how welcome this advice is, but I found the best tip is to stop babying the iPod/iPhone and just enjoy it for what it is. Let it get a little bit scratched on the back, just like trainers and cars get scratches. Once you learn to accept it, life gets a lot simpler, and you won't have to wrap barrier protectives around it when you're using it...