I have to replace an old brick walkway that runs from the front porch to the woodshed/aka garage. There is an electric line that runs from the cellar to the garage and crosses under the walkway at some point. I would like to a) avoid electrocuting myself and b) avoid severing the line. I know there must be some device that can trace the current so I can mark and take extra care where the line crosses, but I have no idea what it's called or where to find one. Any help would be much appreciated.