Since your question concerning sand has been answered I would like to address the "decoration" question.
I have had unlimited success using root balls, driftwood, etc in my ray tanks. The success is due to the fact that I suspend the wood from monofilament and do not allow it to touch the substrate. The rays have access to every square inch of the bottom while smaller fish and plants cling to the suspended wood. No dead spots form, water flow is unimpeded, no food goes uneaten.
Respectfully,
FireMedic.