I am getting a bad back. I want to buld a raised bed garden that is 3ft high so I don't have to bend over to tend a garden. I am thinking of building several boxes that I could grow a variety of vegetables. My question is first of all is this a bad idea? Second, can I put rocks in the box as a base to secure it and then only use about 12 inches of topsoil and compost instead of filling the entire box up with dirt?