75% sounds like a good number. As long as that is enough to include every dune that ever existed and every coastal dune lake shoreline for 1/4 mile.To what end?
At what point in history would you like to go back and "preserve natural areas for future generations"?
1990? !980? 1970? 1950? Earlier?
Was it ok when Grayton Beach was developed at the beginning of the last century?
Is 40% of south walton not enough?
Is Grayton Beach State Park and others along the coast not enough?