There's about three trillion worth of gold, not all of it for sale of course. But there are enough precious metals for a lot of dollar holders to get off said

There's about three trillion worth of gold, not all of it for sale of course. But there are enough precious metals for a lot of dollar holders to get off said currency if they feel it is not in their interest to keep it. Alternatively, they can buy machines to dig for gold or invest in publicly traded gold companies, which also amounts to shorting the dollar. This might not be easy or even possible for China or Saudi Arabia, but it is certainly possible for Egypt and other small countries with US treasury bonds. If a few countries short the dollar, the price of gold in dollars would rise accordingly, making gold reserves enough to accommodate the next few stages of a run on the dollar. Not enough gold? The price goes up.