You honestly think a missile defense system will work. Backhoes are much more creative than that. You will need defense in depth, roaming patrols, as well as air and satellite based monitoring assets.

And then the fibre will get cut by a building crew working on a guard tower.

Ah yes, missile defenses, like the MIM-104 Patriot: https://en.wikipedia.org/wiki/MIM-104_Patriot#Failure_at_Dha...