I dont use locator s when i am working rockpiles .. i no a few lads who have worked ther dogs with collers on in past and have had ther dog hung with the coller...90 pecent of piles you cannot dig as ther too deep ... i have dug many piles to with just listening to the sound of your terrier baying an dug right on top of them... folk say am mad putting dogs in them with no collers but they have never worked rocks ... but each to ther own..