There is not much wire there. That is pretty thin gauged stuff. If you scratch that galvanizing the corrosion is concentrated there and it goes pretty quickly. You probably damaged the galvanizing when you put in the staples. Mine lasts longer than that if I don't damage the coating and if it is up out of the ground so it doesn't stay wet, but, yeah, it can go real quick.
It is also possible the quality of the galvanizing was not real good to start with. Sometimes you just get bad batches. Different companies are going to have different equipment and different people doing it.
I worked offshore in a marine saltwater environment. That is extremely corrosive. If the galvanizing or paint got scratched down to the metal, it rusted real fast right there. For stuff around the waterline especially, we'd use galvanizing and then cover that with paint. Otherwise it went pretty fast. All it took was a little scratch.
