I just realized there is another technique that we use for selecting a safe boondocking site -- when we are scouting campsites in any given area, we take note of the amount of trash on the ground. If there is a lot of trash (especially beer cans), we tend to move away as far as we can, not only because it is unsightly but also because the trash indicates that this particular site is popular with noisy party people. The same with discarded diapers, believe it or not. (Do other parts of the country have a problem with diapers, or is it just Southern California? And what is it with all of these beer-drinking infants, anyway -- if you are drinking so much beer that you have to wear a diaper, maybe you should cut back on the beer?)
If a site is very clean, it means either that people seldom go there, or that it is frequented by more responsible campers. or that it has been picked clean by recyclers. Either way, it's a winner!