Leave No Stone Unturned Meaning

(idiomatic, by extension) To perform a task carefully and thoroughly, not missing any step.

Example: Dryden
  [He] left unturned no stone / To make my guilt appear, and hide his own.
2008 March 11, "Australia cancel tour of Pakistan", The Guardian (retrieved 2 May 2013):
  James Sutherland insists Australia had "no alternative" but to cancel the tour. "We have left no stone unturned in trying to ensure the tour could proceed as planned but at the end of the day the safety and security of our employees must come first."