First thing i put in the bottom of a pot is a heavy stone to keep it weighed down. Now, if the pot were to ever be knocked over by accident, that stone would probably quadruple the damage but...fingers crossed.
I pot most of my orchids in lava rock which keeps them in place...or should. I once thought that I could no longer grow phals as they always seemed doomed. Now that only one of the kids is home, I've started growing phals once more without a mishap.
You know I've tried mounting a few phals lately and they seem to be doing better than in pots. Cause with the medium in pots, you really have to repot Phals. I have been procrastinating and neglecting my phals which were my original plants in the collection. But the Bellina and another one I mounted on pine bark recently are doing very well... whereas the ones in pots, with bark and sphagnum mix, haven't been because I've been travelling and have had to entrust watering to others who have overwatered the plants, the medium is too damp! I've got to repot all my other Phals. Mounting seems to be the safest.