Fitz,
>I like the idea of desecrating a site by placing a stone wall through it but then not having the bottle to completely destroy it for fear of what may happen. I reckon that good old christian superstition has probably saved many a site from total destruction.

You could be right there. The stone walls usually date back a century or two. They were a tad strange about their religious beliefs back then, so perhaps they were scared about desecrating a Pagan site, if only for fear of dark forces.
Also, maybe the ancient boundaries, marked by the circles, held for longer than we thought in these remote northern parts. Let's face it, generally the Cumbrian circles are far less visited (with the exception of Castlerigg) than their southern counterparts, and also perhaps less vandalised (in the broadest context).
Regards,
TE.