Techniques used to locate buried cable have improved drastically since the days when a technician would walk out an area holding two metal rods and watching for them to swing as they detected a magnetic flux. Not only has technology improved, but today’s underground construction or cable placement usually includes a detection tape along with the cables to warn future workers of the presence of utility cables.
Purchase or rent a cable-locating test set. While these are expensive, the low-frequency test set is cheaper than the high-frequency or combo test set. If you're looking for direct buried power lines or lead sheath phone cables, a low-frequency test set will do the job. If you're looking for fibre or you are not really sure what you're looking for, a high-frequency test set will do the job. There are numerous features available, and like anything else, the more features you choose the more expensive the device.
Locate the operator instructions for the device that you are using. Basically, a cable locator is a battery-operated device that will emit a signal through a hand-held wand that will detect underground cables. There is a monitoring device that may be a signal strength meter or digital readout to tell you when you are in close proximity to buried cable.
Search for the buried cable using a grid-type approach. Imagine a checkerboard superimposed over the ground. Follow these checkerboard grids back and forth so that you do not miss any area.
Narrow down the underground cable's route by swinging the wand back and forth perpendicular to the underground cable. By watching the readout on the locator, you can walk forward while you are swinging the wand and it will become apparent to you where the underground cable is routed.
Mark the underground cable location as you detect it. Do not rely upon memory. There are good options for marking the underground cable location such as small wire-shaft flags that are easily stuck into the dirt, or you could even lay a rope or garden hose along the route depending upon the size of the area.