Hmm, bit of a strange one. However, the cairn is part of the boundary limit, in fact the boundary line (between Burley and Hawksworth moor I think) goes through the middle of it, changing from a north-east to south-east in the middle of the cairn itself. Maybe whoever put up the fence was actually trying to avoid the monument (which EH measures as about 26m) but still managed to put it up within the scheduled area. Why they would need to build a fence up there seems a bit of a mystery though – can't see it lasting long.

-Chris