No, I'm determined those cairns will last as long as possible. I patched the worst one with about twenty stones, five years ago, and with hindsight I wouldn't even do that now. The main threat to them is male lambs jumping on them on the summer evenings. It may be best to fence them off when that section of wall is complete - but it will look awful. But you have missed the link with the family of fossils that occurs on the site - the shape of the cairns matches the shape of these fossils. Still no one will enter the Northumberland exclusion zones looking for an answer ...