I like barebottom with driftwood too.. although most of my tanks have a thin layer of sand.
It seems when rays are freshly imported or very juvenile, sand burrowing is a good stress reliever.. however, its nice to monitor how much fecal waste is being produced, allowing it to all blow in a single area from the current, and the driftwood will act as an area of cover.
Same idea with uneaten food.. you will be able to see it easier, it will pile up in one corner, and it's easily syphoned. Un-maintained sand can lead to 'disc rot' and small chunks and bits of food get stuck in there, and if your rays aren't large and vigorous 'pumping' the sand for food, waste will build up.
Most cf. Yepezi types come in skinny and aren't cared for as well as most rays.. might get some prazipro on hand, and be prepared to feed some live worms or ghost shrimp upon arrival.
