I finally started on the cobblestone edge for the lawn. I had to burn away a fairly large tree root before I could get started (I tried to chop it up with my axe, but it was too 'chewy').
To burn the root, I simply fired up some barbeque coal, poured it over the root, and put more coal on top. Then I left the coal to do its thing, which lasted about 3 hours, all the while I dug the trench and poured 'tile sand' into it. Of course, I kept the garden hose ready nearby, should the heat set the grass edge on fire, but everything went according to plan.
I never really realized how uneven the lawn actually is, until I started laying down the cobbles and aligning them with the turf surface. I may - in due course - go back and even out the cobble-rows, filling in some of the 'hollows', but for now, the main objective is to get as much lawn as possible edged!