Natural Gas Firepit on Wood Deck

Hi - I'm building a natural gas fire pit on a wood deck. I'm trying to insulate the wood deck from the heat - even though I really don't think its going to be a huge problem. It's a 12" high pit with a 24 inch fire ring. The fire ring sits 10 inches off of the deck. The pit is made of stones with vents on all four sides at the bottom.

What I'm looking for is a good material to shield the fire ring from the bottom of the deck. People have suggested a piece of stainless steel... but would anything else work? Another metal? Perahps durock or cement board? Or maybe fire bricks? What would be the best idea?

Thanks!

Best idea would be to get a pre-made tested and listed fire pit with a base and everything. It would state in the manual what is safe to do and is not. Then you are not guessing.

I would put a few courses of bricks up to a couple inches below firering and grout it in with fireclay "fireplace mortar" and then fill the remaining area with lava rocks until the firering is completely buried.