I do not get that. The cable company uses a slitting machine that puts the cable in with no trench. It pushes the cable into the ground about 12" where no other wires are. The phone and electrical are deeper, around 30" to 44" around here.
I had mine done and just lived with the wire running across the grass until they came back the following week. It took the guy about 15 minutes to run a 300 foot cable underground.
Why do all that digging yourself? Dig here yourself and hit something you get fined 10,000.00.