Certainly the "carry out" philospohy is gaining in the popular wilderness areas (now there's an oxymoron!) and judging from commment in the US paddling mags and my limited experience on a trip to Canada, the sheer volumn of usage makes the practise essential.
Indeed, one or two wilderness campsites had some variety of dry toilet installed! One beach we camped on had something in excess of 24 kayakers on it. Other more remote areas were clearly receiving relativly heavy usage,
Having said all that, I've never had an unpleasant surprise in Scotland - yet!
As to deep burying, there is a strong school of thought which says that doing so is not best practise as the macro (or is it micro?) biotic thingies that destroy the stuff are not present much below a few cms.
That suggests that the "smearing" technique is the one to use but I do rather think that while it may be ecologically sound, it won't work in a practical sense, except in very lightly used areas.
Shallow burying is probably the best way - a "cat trench". Toilet paper should be burned and adding a small container of meths and a lighter to your toilet kit achieves this easily! I'd suggest marking the ground with two crossed sticks, or stones or something. (THis is a Scouting practise - if it was more commonly adopted it would maybe be a good idea).
As to burying below high water, (using the intertidal zone), this is probably also a good practise, again provided the paper is burnt. Sea water is so corrosive that the material is eventually destroyed and the various beasties in sand/gravel and under sea weed would enjoy their snack no doubt.
The concern re bathing beaches is valid, but then you're probably not going to be using a bathing beach as your intertidal zone anyway.
Certainly I would hope that any form of toileting takes account of water sources - apparantly a lot of the New Zealand areas now have serious gardia contamination.
Probably there is no best/ideal method - each situation may need a different solution and being aware of those solutions is part of the answer. I do think that burning paper is igood practise in any of those solutions though.
A judicious search of some of the online US paddling mags reveals an extraordinary wealth (if thats the word) of info - clearly they have a problem over there. Heres one interesting gem
www.wavelengthmagazine.co...95what.php