The key to sound money: limited in supply and infinite divisibility.
Limited in supply ensures that you cannot counterfeit the money out of
thin air. You want it you have to earn it.
Infinite divisibility makes sure you have enough supply of money as long
as you allow deflation to generate that supply.
ID and deflation together provide legitimate money supply b/c it's like
stock split. Printing FIAT is a fraud b/c it's like stock dilution.
Commodity-based money is the closest thing you can get to sound money.