He left no stone unturned.
More Traditional Proverbs:
A friend in court is better than a penny in purse.Traditional
We set the sail God makes the wind
Traditional
He that cometh in vanity departeth in darkness.
Traditional
An answer brings no illumination unless the question has matured to a point where it gives rise to this answer which thus becomes its fruit. Therefore learn how to put a question.
Traditional
If your foot slips, you may regain your balance if your mouth slips, you cannot recall your words.
Traditional
She's a nut.
Traditional