“万无一失”，汉语成语，比喻十分稳妥，绝对不会出差错。可以翻译为“guarantee complete success; no risk at all; nothing will go wrong; perfectly safe”等。

例句：

由他掌舵，通过这段激流险滩是万无一失的。
With him at the helm, we are a hundred percent safe crossing these treacherous rapids.

为确保万无一失，一架警用直升机一直在空中警戒。
To make extra certain, a police helicopter kept watching from the sky.