Douglas Harper's Etymology Dictionary
Usage examples of "fool-proof".
They tested the twin cylinders each containing a thousand litres of free air compressed to two hundred atmospheres and Bond found the manipulation of the demand valve and the reserve mechanism simple and fool-proof.
The lie detectors were part of Psycho, fool-proof, almost omnipotent in their efficiency.
Like everybody else I wanted a fool-proof system by which I could predict the twitches.