I think kill zones are unreasonable.
I can understand your frustration etc.
Can the fence be improved with a top section leaning outwards for instance.
My view is we moved in to their zone and need to co exist !
from
Porkupine soultions
"The best way to prevent Porcupine intruders is to modify your property to make it unappealing to Porcupines.
Start by building a fence around trees, gardens, and where damage has been most prevalent.
Porcupines might be able to climb fences but a wire strip at top of the fence installed at a 65-degree angle will make it harder for them to climb over.
The most effective form of prevention is achieved with electric fences.
Electric fences should be placed a 1 ½ inch above 18-inch fine mesh wiring fence.
Trees can be protected by wrapping around trunks 30-inch high wire fences that will reduce their feeding damage."
In my research from Australia I was surprised to see they are considered rodents and also are protected in some areas