I've been watching this trace for a while and remember seeing utility
guys tracing underground services with a device. Could it be like one
of these?
http://www.electrical-contractor.net...?source=google
It will detect services down to 10'.
This site also talks about detecting breaks in underground irrigation
systems and specificly about finding breaks."The
valve-locator/wire-tracker can be used to trace the wire path, locate
valves, locate splices, and locate damaged wires."
http://www.igin.com/Irrigation/groundwiring.html
For instance this unit uses a number of different frequencies:
http://www.professionalequipment.com...qx/default.htm
Richard