I have been using 2 pieces of brass rod to locate underground pipes and wires.
I first tried it about 10 years ago with a couple of coat hangers when I was looking for the septic tank for my old farm house. I was able to find the tank and clay pipes on my 1st try. Then I started walking back and forth across my back yard and found some old abandoned wooden pipes, underground wire, and my polypipe waterline from my well.
Over the years I have used this technique to find mower parts that had vibrated off while mowing my fields, tools that were lost, and have found many pieces of junk. I have also found jewelry and coins.
At work, I use ferro-magnetic locators, ground-penetrating radar and radio location equipment, but I also use a pair of rods.
I don't know why a couple of bent rods work. My theory is that somehow I am locating slight disruptions in the earth's magnetic field.
There is a fancy low-tec commercially available device that works somewhat like my brass rods, but I doubt if it works any better. http://www.farwestcorrosion.com/fwst/instrum/magnetomatic.htm