There are various ways to scan for sub-surface services before you dig. I'm not sure how well fibre is detected by these methods (Cat-and-Genny wouldn't be much use; no idea how effective Ground penetrating Radar is with fibre).
Our gracious hosts had a lecture/video by Ordnance Survey on utility mapping challenges. UK & probably RoW have depth management, so water/sewer deepest, and newbie fibre the shallowest. Which kind of explains fibre cuts where utilities dig through fibre to get to their own stuff.
But there can be locator wires embedded in fibre cables, or in ducts to help with cat & gen tracing. Not every operator seems to do this, ie CityFibre's been laying pipe around me & using a mix of polypipe and microducts.. I didn't see them running locator wires though. But shallow depth helps GPR, which works by sensing density changes, so if there's ducting, it should be able to sense the voids.
Biting the hand that feeds IT
