He saved the gold by destroying it
and then placing it in plain sight.
A true story of how a scientist deceived the Nazis, from Robert Krulwich at NPR:
It’s 1940. The Nazis have taken Copenhagen. They are literally marching through the streets, and physicist Niels Bohr has just hours, maybe minutes, to make two Nobel Prize medals disappear.
These medals are made of 23-karat gold. They are heavy to handle, and being shiny and inscribed, they are noticeable. The Nazis have declared no gold shall leave Germany, but two Nobel laureates, one of Jewish descent, the other an opponent of the National Socialists, have quietly sent their medals to Bohr’s Institute of Theoretical Physics, for protection. Their act is probably a capital offense if the Gestapo can find the evidence.
Inconveniently, that evidence was now sitting in Bohr’s building, clearly inscribed "Von Laue" (for Max von Laue, winner of the 1914 Prize for Physics) and "Franck" (for James Franck, the physics winner in 1925) like two death warrants. Bohr’s institute had attracted and protected Jewish scientists for years. The Nazis knew that, and Niels Bohr knew (now that Denmark was suddenly part of the Reich) that he was a target. He had no idea what to do.
Read more: Dissolve My Nobel Prize! Fast! (A True Story), Krulwich Wonders, NPR>>