Rats in pull pits sometimes chew fibre. Power cables tend to kill the rats, but on fibre they just keep munching. Steel tape armour is fairly resistant, but once the rodents attack the outer sheath the exposed steel can corrode. The best solution is keeping the ducts sealed and the pull pit lids secure, then the little bas___ds can't get in.
The typical failure we see on single mode fiber is from too much optical power. If you 'smoke' a fiber with too much power (milliwatts) you can burn a small hole in the end of the fiber (similar to a divot in golf). This can have some nasty attenuation/reflection/refraction effects on your signal even after the power is turned back down.
The life tome if fiber cable, barring rats of backhoes, is depenand on the bend radius and any dynamic movement. Other issuses are thermal shock. This has all be calculated and enforce by TELCORDIA. All fiber race ways are made to maintain a minimal bend radius.
Resently, these radii sepcs have change though. Newer sysetems running at longer wavelengyths are supseptable to polarization anomalies which are produced in the fiber during a bend. In short, the bending stess producess non symetrical index of refraction changes.
As long as the above criteria are met, the fiber will last as long as a pice of class, or glass bottle baried in the ground
