Fiber cables are inherently very reliable, extensible and secure. However, my major concern is vandalism of any cable, fiber or copper. A razor blade can inflict major damage, and the chances of being caught are very slim. There are several ways to physically protect cables. Put them inside metal conduit, which most fire codes require anyway.
Utilities often pressurize the conduit with a special gel to keep out water and oxygen.
This is equally effective for inside, aerial and underground cabling. Any tampering drops the gel pressure, which is immediately detected but sometimes hard to locate. Problem here is later cable changes, if your cable plant isn't well planned. Cables inside a well-grounded conduit cannot be tapped and are shielded from outside magnetic and electrical fields that can disrupt transmissions through copper. Add proximity detectors along an entire cable path.