The alternative way is time domain reflectometry.  You need to be able to disconnect the ends of the cable and then send electrical pulses down it.

If you know the electrical properties of the cable, it's possible to calculate how far away the broken end is by how long the signal takes to reflect back.

Phone companies do this to locate breaks in their telephone wires.

If you have a meter that measures  capacitance you can read the capacitance of the broken core to the armour and other cores in parallel from both ends,  the capacitance will be proportional to length. This may not be possible if the break has a significant resistance to earth, but then you can put a voltage gradient along the armour, and look at the voltage that appears on the defective section . This only works if there is only one well defined fault, rather than a long damged region.

Do not overlook the obvious - faults may coincide with new fence posts, or building works, tree roots or other sources of landslip...

Mike.

The TDR method is used by DNOs every day.I like Mikes capacitance idea though, but the TDR works on any cable (single or multicore) and whether there is armour or not. Because we can measure time very accurately and with great resolution the TDR is best. It can easily get to within a foot of a fault, 500m from the end. Speed is about 1.5ns/foot for most types of cable, as a quick guide. You can do the same with a fast pulse generator and a fast oscilloscope.

The TDR method is used by DNOs every day.I like Mikes capacitance idea though, but the TDR works on any cable (single or multicore) and whether there is armour or not. Because we can measure time very accurately and with great resolution the TDR is best. It can easily get to within a foot of a fault, 500m from the end. Speed is about 1.5ns/foot for most types of cable, as a quick guide. You can do the same with a fast pulse generator and a fast oscilloscope.