Do you have any buried utilities in your area? If so, call and get them to come out and mark their cable paths. Then take pics of what they marked.
A friend of mine was replacing a wooden fence, and used a power auger to dig out the existing post holes to a greater depth. As it turned out, the telephone path was marked incorrectly, and a 50-pair cable that was buried about an inch under one of the existing holes was chewed up by the auger. Phone service for his entire neighborhood was out for 4 hours. The guys from the phone company were REALLY pissed about having to dig a huge hole and patch up the cable. They told him he would be getting a bill for their labor. He snapped some pics of the incorrectly marked cable path, but by that time the paint was pretty hard to see due to all the digging and stomping around for the cable repair.