Don't put it in your zipper pockets in pants. If you fall on it, good chances are screen will shatter. If you tend to fall on your chest area a lot (not sure why..?), don't bring it onto the mountain. And use above comments, case with a plastic bag.
pointless story/ I lost my Blackberry 4 times last season, and it got returned to me within like 1 day to 1 hour. (I'm not an idiot, Burton jackets zippers are rubbed with butter before giving them to the public and unzip a lot.)/Fin