How big should my pot be to grow a healthy zucchini?

I have been gardening mostly in containers for about three years now, and the "easiest vegetable" always seems to be my Achille's heel. If the slugs don't get them, something else does. I think perhaps I am not giving them enough room. Has anyone had success with zucchini in a container, and what were the measurements? Width/Depth/ and did you mix in any rocks or bark to promote drainage? I garden organically.