That picture of the fence is straight vertical. The fences that the government installed at Cape Canaveral were vertical, then curled outward. Alligators cannot climb a fence upside down.
I know the type fence you are talking about . It only keeps the smaller ones out . The dangerous ones are in the 8-9 foot range and they can smash a fence and are still agile .
The problem is that there are too many gators out in this size range .
Trust me it was not 4-6 footer that took that kid of the shore . At that size they feed on fish.