WordNet (r) 3.0 (2006):

leave no stone unturned
    v 1: search thoroughly and exhaustively; "The police left no
         stone unturned in looking for the President's murderer"

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "leave no stone unturned":
   carry through, clear the decks, comb, consider every angle,
   exhaust every move, follow out, follow through, follow up, forearm,
   go all lengths, go all out, go for broke, go the limit,
   guard against, hedge, leave nothing undone, leave out nothing,
   look all over, look everywhere, make every effort, make sure,
   make sure against, not relax, not rest, overlook no possibility,
   overlook nothing, play safe, prepare for, provide a hedge,
   provide against, provide for, rake, ransack, reef down, rifle,
   rummage, scour, search high heaven, see it through, see out, shake,
   shake down, shorten sail, spare no effort, spare no pains,
   take measures, take precautions, take steps, toss, turn inside out,
   turn upside down