not saying parkrangers cover every foot but they are very good of noticing things that look out of place......guard the same mile of woods for 10 yrs you get to know it pretty well also the place "people try" that look very hidden....

remember when your in pres of park authorities they probably know the area much much better than you do.........
example ever hike with a very experinced guide......they will point things out at 150 yards that the ave person has a hard time seeing up close......mostly by the disturbances in the area