The sheep are now living in the "Millennium" birch wood, down towards the lake. We have fenced off an area that allows them to graze under the birch trees down to the water and across into the neighbour's field. We just used regular sheep fencing and wooden posts. So far it seems to be enough to keep them in.
Having severly pruned the neighbour's oak tree, they are now nibbling the tips of the curly birch branches which are within reach. They don't seem to be using the trunks as scratching posts.... yet! They are doing a fabulous job of keeping the grass down around the trees, so soon we will give them a bit more space.