I've stopped using anything in the bottom of the pots - only potting mix and the potting mix does not fall out, nor do I usually have drainage problems. I have some pots over 20" that didn't seem to have enough holes in the bottom so I've drilled holes as close to the bottom as I can get but in the sides. This way I know they're draining because I can see it. I put all my containers on gravel, pavers, elevate with a couple of bricks, etc., and never let them touch actual ground - no grass no dirt - mainly because of slugs and other undesireables, but also the drainage problem. My actual ground is all concrete-like clay which doesn't absorb anything so all my gardening is done in containers.
