Holy COW folks, you have GOT to read the document!
They Cite Warren vs DC ("the government and it's agents are under no general duty to provide public services, such as police protection, to any particular individual citizen"
) and they also acknowledge that there is no way 3,000 NPS officers can realistically police millions of acres of parks.
I am literally STUNNED to hear that admission (though they still deny that Heller had anything to do with their decision...ya right, pull the other one).
(warning, pdf file)