Thats if they even see the fence until its to late. It you might have a point with a single but the muti engine machines if an engine goes bang they are not quite so controllable in direction. Remember they are not pref A machines so are not garanteed to climb after failure and may limp a few hundred feet before hitting the deck.
To be honest I doudt very much if the airport even knew the re-bar was being used in the fencing.
The farmer will have had a requirement to shaw up the fence because its boggy as hell around the lights. Fencing posts etc will be expensive cause they will have to be shipped in. The re-bar will proberly be spare from some other project. Once its been sitting for a while you can't use it for its intended purpose because there won't be any paperwork for it. Farmer would have been dead chuffed he found a use for it and his fence is srurdy as anything.