Cool site, unfortunately I am in the South African part of the handle at the minute. You might be interested in using photosynth, it picked up the medieval rabbit pens quite nicely on top of Pilsdon Pen in Dorset when I flew it a couple of years ago
Have a look at the point cloud, which you can extract and correct to create a DEM.
Flying lots of surveys through changing seasons might also be a good idea. As I say will watch with interest.