Fully cover?  I don't think anyone would make a case to fully cover the power and volume buttons.   But if you use a back cover, it will make the buttons recess further and won't be able to accidentally press them.  I have a Ringke back cover and the buttons are about 2mm away from the back surface.  I could install the cover upside down to cover the buttons but it will also cover the camera and flash along with charging and headphones ports.