There is a student at my school, who is currently struggling keeping his hand up when he kicks. This is especially prevalent when roundhouse kicking. His arms either drop to his side or his guard opens up and his arms go into a position where it looks like he's flexing. Are there any drills that help with keeping your hands up? I know it's common for beginners to move there arms a lot when kicking, because they haven't developed control of their bodies. Anything helps.