Thanks to all for these great ideas. I envision my suitcase expanding with "search contingencies". Love the idea of using water on a light stone; had never considered the issue of moss. How does one overcome that barrier? Hmmm.
I've got a few grave sites to visit in Aberdeen and other Chatters have been most generous in helping to identify the locations of those. All are in mapped yards - though not the same yards.
An island historian (and sometimes visitor to the Inverness RootsChat Board) has provided some guidance with respect to Benbecula - apparently 3 grave yards there, but one is under an airport runway (covered up in a hurry in WWII when defences were paramount as I understand it). Another one, very old, exists but has no markers. The third dates back to about 1850 (if I recall correctly), is still in use, is apparently reasonably well kept, but never mapped. It is the largest of the three on the island.
I've got burials dating back before 1880 on South Uist, but haven't yet done any research on those yards. The sites might be too weathered to be of much value. Perhaps I'll be proven wrong when I visit.
While I know I've family buried in the Outer Hebrides, I have no idea if any have stones, but I'm on a quest so am compelled take a look.
TX again to all. Your insight is much appreciated.