Trust goes a long way, but at some point, if you’re going to sponsor a stable currency, you must put up or shut up. Somewhere, you have to actually have a shitload of gold in the basement. Around the time of the evacuation from Dunkirk, when the Brits were looking at an imminent invasion of their islands by the Germans, they took all of their gold reserves, loaded them on board some battleships and passenger liners, and squirted them across the Atlantic to banks in Toronto and Montreal. This would have enabled them to keep their currency afloat even if the Germans had overrun London.