I always made sure to hide my iTouch really well in my backpack during my P.E and weightlifting classes. Some kids got their phones/ipods stolen because they would just leave them on the shelves and assume that since they are "cool" nobody would touch their shit. (Seriously happened to one of the varsity kids in my class. He threatened to kill the kid but he never found out who it was.)
Or just get $5 padlock and end all of these problems?