Hi, What type of fiber are you using ??
A "dead loop" would prevent stretch,
I usually slide heat-shrink tube (the thick glue-compound one is better) along the fiber then you can clamp it with light hose clamps or cable clamps.
Friction between heat-shrink tube and mast is enough to prevent fiber from slipping , even with low clamps compression
This at least at netmetal near end, along the mast you could use the methods used with antennas cable
Fiber has not to be pulled in its job.....
Are you working on 44 A-class ?