I haven't heard that one. The story that is usually reported is that Sec Def Schlesinger told the Joint Chiefs and others that if they got any crazy/extreme orders from the President that they should check with him first. It has not been actually confirmed that he said this (the only accounts of this seem to come from Schlesinger himself), it would certainly have been an order without any legal merit (the JCS would not have been obligated to follow it), as the Sec Def does not have the power to do that (and is not, as far as I can tell, even in the nuclear chain of command). I tend not to talk about the story because if it did happen, it was illegal or meaningless, and if it didn't happen, well, then it didn't happen. There were certainly fears that Nixon might do something stupid in his final days of the Presidency. I am, again, not sure of any legal basis by which one would "confiscate" the nuclear football.