There is a fully gold-backed stablecoin, called Digix. It is regularly audited, and the gold backing the coin is redeemable from the issuer. The problem with it is that it's, just like any off-chain collateralized crypto, fully centralized.
I've written a series of articles about stablcoins, part 2 was this: https://medium.com/datadriveninvestor/gold-on-a-block-stablecoins-part-2-7928598b282d