foolproof

It’s always a good idea to wash produce for that reason, but it’s not foolproof.

It is remarkably uncomplicated and virtually foolproof.

While 2FA enhances security, it can also foster a false sense of confidence. 2FA seems foolproof, leading many people to pay less attention to other security practices, like using strong, unique passwords for each account.

"That was clearly a foolproof plan given I'm reading those texts to you right now," Oliver joked.

Also, safeguarding checks are not foolproof because they don't necessarily mean that suspects can't move into other organisations and perpetrate abuse.