Hopefully I won't be repeating something already written here----One poster wrote about the items left on PUBLIC LANDS both on the border and in other parks.
In North Idaho, some very determined person (people) climbed the tallest pine tree in the forest and placed an AMERICAN FLAG on a tall pole out the top of the tree--complete with a solar panel to illuminate the flag at night. It is very visible from I-90, and quite pretty to see.
The U.S. Forest Service wanted to hire some company to remove the "private display" from the tree. No one would climb that high to the point where the pole was placed, so it's still there (last I saw). The government position was that no private property be placed on public property, like American Flags on U.S. owned soil, or geo caches, etc.
My point here is that maybe the Natl. Park Service get the U.S. Forest Service to put a stop to the practice being allowed on the border!!