When you say "audit the Fed" what exactly do you mean? Like a financial audit?
Count the number of gold bars. Determine which of the gold bars are just gold plated Tungsten bars. Subtract the number of Tungsten bars from the bars in the depository. This sum should equal the total number of gold bars you really have. Keep this number secret. If the real number of real gold bars was known it would cause a collapse in the economy.