Literally, it means you have turned over and looked beneath every possible stone. Idiomatically, it means you've looked everywhere you could and have done everything you could to try to solve some problem.
Dev: Didn't you find my book yet?
Ted: Believe me, I've left no stone unturned and did't find it.
("Leaving No Stone Unturned" example)
Ted: Believe me, I've left no stone unturned and did't find it.
("Leaving No Stone Unturned" example)
by AgentFire October 3, 2010
Get the Leaving No Stone Unturnedmug. by indierep February 20, 2011
Get the Stone Unturnedmug.