Hi Rob
A PhD student at the University of Portsmouth was studying the landslides of the Dorset/Hampshire coast and may well be able to point you in the right direction.
His name is Andy Gibson. Possibly Dr Andy Gibson by now!
The university number is 02392 876543 - ask for Andy Gibson in the geology department. If he is not there then either Mike Chaplin or Andy Poulsom might know his contact details.
My tuppence would be to say that lowering the energy of the waves would certainly reduce the erosion of the toe of the feature but would not account for loading at the top end nor the effects of hydrostatic pore pressure (which can 'lubricate' the failure plane and allow movement).
Another (ex-Portsmouth university) expert in this field is Dr Bill murphy, although his interest in landslide activation is more earthquake-oriented.
Dr Bill Murphy
Course Director: MSc Engineering Geology
School of Earth Sciences,
University of Leeds.
Leeds.
LS2 9JT.
0113 233 5232
w.murphy@earth.leeds.ac.uk
Good luck!
Adam B-Browne
Hydrogeologist
URS (Cardiff)