Johnson's Magnetic Locators detect ferrous metal and areperfect for locating survey corner markers, PK and Mag Nails, valve boxes and curb boxes, steel and iron pipes, well casings, steel tanks, lost tools or even downed and burried fence lines. The lightweight and rugged construction is suitable for harsh field conditions. Magnetic Locators from Johnson can detect buried items from one foot up to 10 feet deep. Each can be submerged up to 75 feet under water.