油ゆ断だんも隙すきもない

expression

one must be constantly on guard; one cannot be too careful

Used to warn that someone or something is so formidable or tricky that you must never let your guard down. Often followed by the person or thing requiring caution.

• 彼かれは油ゆ断だんも隙すきもない相あい手てだ。

  He is an opponent against whom you must never let your guard down.

• この問もん題だいは油ゆ断だんも隙すきもない。

  You cannot be too careful with this problem.