Mike - I think you are mis-interpreting the type of off the beaten track that OP was looking for.
The vast majority of rural Cambodia is safe but care should always be taken when straying off the tracks that are used by the locals (or in some cases do not stray off them).
mike-asia said, "I m not so sure I would like to get too much of the beaten track in many areas, particularly those closer to the borders and formerly KR dominated." Too much of a sweeping generalization, First all of Cambodia was KR dominated, secondly, I live approx 30 kilometers from the Vietnamese border and there is no danger from mines since the KR fled immediately from the advancing troops. Planting mines takes time and is a defensive measure. The area is heavily farmed and considered safe by locals. There was de-mining years ago to be sure, but mostly for bombs dropped by either the Lon Nol air force or the US air force.
As for snakes, yes we have them and one must exercise caution since the Ministry of Health purchased anti-venoms from India because they were cheaper(and probably made a few bucks on the side to boot)rather than from Thailand where the snakes are more related to Cambodian species. So, even though there is a hospital nearby, a victim would have to go to Thailand for treatment-if they lived that long. Again, we have them, but don't imagine a National Geographic scenario where they are dripping from the trees. In fact there are fewer and fewer every year since the locals eat them.
Al re the pm, I have nothing add. A fine job was done by all.