Ishmael,
The problems with cairns and walkers are nationwide. The only real trouble arrives when there is interference with an ancient cairn.
Walkers and climbers in Cumbria have always erected strategic cairns at key places, to aid navigation in the appalling weather frequently experienced on mountains. Unfortunately, the mentality of the modern walker has rendered this useless. Cairns appear, in some instances, every six feet or so, rendering the strategic cairn, perhaps signalling the only safe escape from a ridge, useless, as the cairn is now lost in a sea of other cairns.
Unfortunately, a lot of prehistoric cairns in the Lakes are robbed by unthinking persons unknown to make a line of cairns as far as the eye can see.
The other problem is the re-arranging of prehistoric cairns to form shelters from the elements. Again, sadly, examples of these are seen throughout the Lakes. The greatest regret is that most of these cairns haven't been excavated.
Cheers,
TE.