A very smelly topic, but IMHO, a very timely one. Sadly, I have witnessed myself the foolish habits of some campers in this regard.
As an ex military person, where I gained my knowledge of the finer arts of long drops, I'm always disgusted at what I see being done at camp sites. We go to the great outdoors to enjoy what it has to offer, yet some idiot has cat scratched the surface, dropped their load, scratched it over and took off. Only to have someone like us turn up and set our camper right over the cat scratch without knowing until you STEP in the mess. Or dunny paper all over the place and human Shit behind every bush.
Getting back to your subject. I've discovered the reason what Folks do as you've posted.
Apparently they do not wish to use the dirty smelly dunny's the Parks have provided, thus they insist on using their own, most times very questionable set ups.
Of course the FACT that the dunnys is dirty and smells in the first place is because people are too stupid to close the lid after use, also their kids usually make one hell of a mess in such toilets, parents reckon "it's not our so why should I care".
AND, of course in some parks the employees are a little lax in cleaning them regularly, so it all adds up.
I would NEVER, dig a hole anywhere near a established toilet, or in a park anywhere. NOT ON. Even if it means carrying wipes and air freshener to clean the dunny and spray around a bit before use.
IF you MUST dig a hole, PLEASE dig it deep, at least three to four feet, more if possible, and YES, the foul ground sign should be obligatory.
One time it took me 6 days to dig a hole five foot deep. It was bloody hard clay, and the shovel simply bounced off without any effect. So I chucked in a bucket of water every day, allowed it to soak in over night, went back next day and dug it out until it again became too hard, chucked in another bucket of water and repeated the process. After 6 days it got to an acceptable depth never to be a bother to anyone, and allow me to return to same site again and enjoy.
