The Thornborough Henges 71
Image by Jane
The Thornborough Henges

Setting

That's why I think the viewshed will be a lost cause.

Well it sure as heck is at Avebury, with a village on it and at Stonehenge, where the MoD, Highways Agency and maybe shortly EH have intruded into it!

That's right. How many houses in Avebury village are listed buildings? The most you can hope to do is protect undeveloped moorland. Where land has been farmed and built on for centuries - no way.