The problem with relying on inspection to detect whether your cable ties are starting to degrade enough to be vulnerable is that YOU are only going to be out there OCCASIONALLY checking them (and will probably not test them to the limits of their strength, as that tends to be real hard on the fence wire etc), whereas the predators are out there checking them more or less constantly (a lot more often than you yourself, anyhow, and a lot more vigorously).
So, the first sign of weakening is apt to be the presence of a pile of bloody feathers one morning.
Just saying,
Pat