The worst I've had is in a pulp and paper mill, 11kV power cable with 40mm (1.5") of asphalt over it.
About six months before I started there one of our guys was looking after a drainage job. He had got the excavation permit. They found a cable in the way. The mill IT guys said it was redundant and to cut it. He said "you do it", they did and the whole north end of the site, log yard, chip reclaim, debarker and chipper lost comms. It was a fairly new fibre!!