Mark, I think each company used to send their own personnel out to mark the lines, but it's sure changed in the last 10 years. Our water company still sends their own people, but the phone company uses a contractor who does nothing but mark lines. And when I was doing the gas leakage surveys and the gas company had to have electric and/or phone lines marked before digging, it was sometimes the same individual (contractor) who marked both. I assume it's different in different parts of the country.
And I had to do a lot of "probing" (usually about 18" deep) with a 5/8" steel rod and slide hammer affair to "center" underground leaks; i.e., figure out the most likely spot to start digging, and my company told me to expect to break a phone line or electric line someday and to not worry about it; that's what our insurance is for./w3tcompact/icons/shocked.gif Well, as it turned out, I never broke one, but I knew of it happening to another employee on the same job I was working once.
Of course, the possibility of hitting an electric wire was the reason the slide hammer for punching holes had a rubber coated handle and the tip was ball shaped instead of pointed (might slide past a wire without breaking it), and the pickup tube, or probe, on the combustible gas indicator was fiberglass instead of metal./w3tcompact/icons/laugh.gif