This is a very interesting thread, not sure if able to respond as it is specific to the Highlands - the first time I travelled through the Highlands in 2007 the guide and driver (who was a Fort William man) pointed out the occasional memorial cairn along the roadside, can't recall who they were for though.

If I could add something further south - was in the small Oxfordshire town of Wantage yesterday and came across the Betjeman Millennium Park- which a small wooded/wildflower park with a contemporary stone circle in it. Lots of other sarsen stones dotted around the poetry sculpture trail (circular and compact). A fabulous memorial to a great 20th century poet ... I thought.