The link above will take you to the Geotech Report determining the cause of the slip on the Dun Mountain Trail. Some of the concept maps and photos are very damning, and leave little doubt that;
a) the area was known to be high-risk before construction began
b) the alignment of the fence track was moved to within the 50m minimum separation recommended by the Resource Consent.
The Trust has therefore deliberately and knowingly endangered a recognised historical asset, supposedly because the original alignment was unfeasible, and breaching the distance would be less expensive than maintaining / increasing it. Sure hope they’re kicking themselves now… as I imagine the repair costs might just outweigh the additional costs they avoided!