Used to work for a few ISPs. 90% of the fiber cuts that were experience while I worked there were from municipal construction crews who either weren't fully paying attention when working around fiber lines, or didn't know they were there in the first place.
The lines are supposed to be known/marked to some extent but you can't avoid the human factor.
In our worst case the same city cut the fiber line in multiple places over the course of a few weeks. Our crews would finish patching one fiber break only for the same (city) crew to cut it again a few hours later.
I wasn't on the ground so I don't know exactly how they managed it, but it was a real headache for us to manage on the customer end.
The lines are supposed to be known/marked to some extent but you can't avoid the human factor.
In our worst case the same city cut the fiber line in multiple places over the course of a few weeks. Our crews would finish patching one fiber break only for the same (city) crew to cut it again a few hours later.
I wasn't on the ground so I don't know exactly how they managed it, but it was a real headache for us to manage on the customer end.