Until society allows one to kill these "people", hang them at the trailhead and nail a sign to thier forehead that says "litterbug"or "snagger" or whatever. There will continue to be unpleasantness experienced on the rivers.
Shoot, shovel and forget is beginning to make more sense. Or maybe we should just ask them nicely not to crap in the parking lot.
You might get the impression I'm just about fed up with some of the pigs that I have to share the outdoors with.