Here's a tip to help play the game.
Many utilities have a thumper in their arsenal of primary cable fault locating equipment.
This is because it is usually considered to be the most important first test set after a Megohmmeter to acquire in dealing with primary cable faults. Although they shine in most direct buried secondary fault locating tasks, they will be severely limited with non jacketed concentric neutral primary cables - which is the true domain of the thumper. This is because most primary cable faults - especially on modern XLPE cables tend to be high resistance faults. This makes it hard for significant ground gradient current to find it's way out to soil - in fact, it prefers to travel along the bare concentric. Also, the plastic dielectric is extremely resilient.