The phrase "foolproof plan" is correct and usable in written English.
You can use it to describe a plan that is designed to be effective and without the possibility of failure.
Example: "We have developed a foolproof plan to ensure the success of the project, leaving no room for errors."
Alternatives: "fail-safe strategy" or "foolproof strategy".
So, I thought, we would need a foolproof plan.
So Mark takes a load of tanning pills and carries out this foolproof plan.
I reminded myself of my foolproof plan to quit smoking before I turned thirty.
O'Callaghan explained that what was originally thought to be a foolproof plan quite quickly turned into a disaster.
Trump has said he has a "foolproof plan" to defeat Islamic State, but has declined to offer specifics.
It's yet another absolutely positively foolproof plan in the movie that's just not going to work out.
Players have foolproof plans for improvement — or, at least, the confidence that everything will be great.
Soon after, two fellow employees drew him into an identity-theft scheme, he said, one of those foolproof plans that never are.
However, as is the very nature of China's communist regime, the Party surprised the world when it came up with one of the most elaborate and foolproof plans to censor the entire interweb and regulate what each Chinese citizen saw, read and shared over the internet, what is now known as the Great Firewall of China.
Beginning his freshman year of high school, Fish has "a foolproof multipoint plan for popularity and success".
It was, boasted Kreuger, an almost foolproof business plan: the loans were secured against revenues that he controlled; the monopolies, meanwhile, ensured generous returns.According to a 1930 article in Foreign Affairs, Swedish Match struck such deals with nine European states and three South American countries in the 1920s.
