about 2 years ago my supervisor was in a hurry to get off work and decided to throw my backpack at me cause getting out at 18:01 was obviously "dawdling"
the landing dented my lower left palm rest, halfway killed my DVD burner (it reads but can't burn), and my track pad has been overly sensitive since. it was 1 month past the 3 year warranty.
so yeah, how to prevent it? it's basically like driving a car, shooting a gun, sky diving...don't get into accidents. don't do stupid crap like leave it on the edge of table, keept it near coffee when you (people around you) have two left hands/feet, don't let people borrow it etc etc etc.
however, after it got dented i got over my phobia of keeping my laptop in pristine condition and started using it like, you know, a normal person