They can try, but they have to find it, first. It will be much harder for them to confiscate the gold than it will be all those CDs, IRAs, 401Ks, etc. that are conveniently sitting in banks that are 'too big to fail'.
It will also be harder to find the gold than it will be to find your house, farm, ranch, or other real estate that has been surveyed, plotted, and recorded in the county records since long before any of us were born.
I just got my RE license and became a member of the multiple listing service. We get access to property tax records through MLS (it is public record) and the stuff that the county assessor posts online about your house, how much your mortgage is, any property you own in the county, etc. is shocking.