As a goat owner I can confirm the untruth of goats eating anything. In my experience they only eat the things you don't want them too and leave the rest! Whilst on the subject is there anyone else on the forum keeping goats? I have a fine billy available for breeding or I would be interested in swapping Billies for breeding purposes.
Bruixot

PS Donkeys seem to be better at clearing undergrowth and thistles in my personal experience.