There are some metal detectors that can detect as deep as 8 - 10 inches in the ground like the Bounty Hunter Land Ranger pro. The Limber Wizard 5 Nail finder can go as deep as 5-10” in the wood depending upon the size of the metal object present inside the wood. The bigger the metal present inside, the detection can be done from more distance and the smaller the metal the closer the detector should be while detecting.