John,
"The Governor was duly advised on how to deter future helicopter visits, as were other prisons. To this day, no prison has bothered to string wires across open spaces."
In UK they have got this all covered these days. They put red circles on the chart; that is apparently sufficient to prevent helicopters from landing.
Just like the exclusion zones recently put over London, which prevent terrorists from overflying.
Was it your good self who fooled 'em?
