Can metal rods detect underground wires? Until not long ago, I was working in the drilling and infrastructure business. Some people I was working with used metal rods as a "quick and dirty" method of detecting underground wiring, before bringing in the full power Ditch Witch.
What they did was to take two metal rods (brass or copper, not sure) that are hanged on some pin so they can freely spin horizontally. The person moved it around the surface until the rods aligned with the (supposed) wiring. Surprisingly, this worked.
This is not some magical detection of water with wooden sticks, but rather light weight metals (possibly) interacting with an electromagnetic field generated by underground wires carrying electric current.
Some more info: one of the men also used this to "detect" concrete sewage pipes. I don't see why this would work. He also knew there were underground wires around, just not the exact location.
Can underground wires cause horizontal rotation of metal rods, held above the ground?
 A: Yes. Current running through the underground wires create a circular magnetic field along the axis of the wire. Any moving metal structure in the proximity of the magnetic field will induce a current in the metal and this will create an opposing magnetic field. The opposing magnetic fields create a torque similar to the way torque is generated in a DC motor, and this will cause the metal to rotate towards a point of equilibrium, which for the rod is when it's parallel to the wire - assuming the run of wire is also straight.
Incidentally it was the movement of current carrying wires in close proximity to one another that led to the discovery of electromotive force.
A: The phenomenon is maybe due to small disturbance in the magnetic field of earth. Rods will move the same above any area, where ground is mostly uniform but there's a small touched up patch, like a covered up ditch or a cable or drainage pipe laid down with a plough, etc.  
A: No, there is no scientific reason under ground wires would not cause "witching rod" to cross. Witching is a "domain" of Dowsing, a type of divination, in which resources underground are discovered.
Wikipedia details some of the experiments that demonstrate the ineffectiveness of witching (and Dowsing) methods. The results of the work typicality find witching, (and Dowsing) to be no better then random change. The  Ideomotor phenomenon is likely what causes the rods to cross.
Dowsing is not scientific or effective in controlled test, however there are many anecdotal claims in support of these processes. Take this wild article from Popular Mechanics or this write in to the Guardian . It is possible in the future science will justify the processes of dowsing and witching, but until these processes can be explained they are classified as divination.
A: The disturbance of the magnetic field of undisturbed land causes the polarity of the iron in the ground to change. The witching does not find the wires or pipe, but the disturbance of the magnetic field of the natural land 
Even engineered compacted full material will display the same results. Polar alignment occurs immediately upon placement if the material. The ditch displaced even  this material. 
