It was illegal to privately own actual gold anywhere in the world as a US citizen between 1933 and 1975. That's absolutely an approach they could take.
Well, that depends. You could have gold teeth, and jewelry, so if you were really determined... though having all your teeth hollowed out and filled with gold doesn't strike me at scalable strategy, at least not unless you have a lot of kids. But all that was also only because we were on the gold standard. Which, contrary to gold-bug belief, wasn't immune from currency manipulation. The US government arbitrarily increased the value from about $20/ounce to about $30/ounce at on point, making the government suddenly richer in a way not much different than printing more money in today's fiat system.