In the Huffington Post, an environmental activist repeats an urban legend:

In 1968 Richard Nixon campaigned on his “secret plan to end the war in Viet Nam”. Of course if he TOLD you the plan, you wouldn’t have to elect him so he was keeping it close to the vest. Epilogue: There was no secret plan. At least not one that worked.

The passage links to a History Channel “documentary” that makes the accusation without offering any evidence.  Of course, there is no evidence, because Nixon said no such thing.  As speechwriter Ray Price explained in 2002:

That myth had its origin in the New Hampshire primary, when a wire-service reporter, new to the campaign, filed an article misinterpreting one line of Nixon’s standard stump speech: that “a new administration will end the war and win the peace.” We on the Nixon staff immediately pointed out, to all who would listen, that he had not claimed a “plan.” Nixon himself told reporters that if he had one, he would have given it to President Johnson.

It was his rival for the nomination, Gov. Nelson Rockefeller, who derisively added the word “secret,” and, on that basis, reporters and commentators ever since have snidely accused Nixon of claiming a “secret plan” he did not claim and denied having.

Frank Gannon has referred to the “secret plan” as the “Dracula of canards.”  More here.