Peter Allen from Mastodon Valley Farm does the grazing at Mark Shepard's New Forest Farm. He has a really interesting insight on the usefulness of prickly invasive shrubs as a protection against grazers. He lays his thoughts in a really good article.
i love this line of thinking. i agree, i also like the dense thorny hedge plants that propogate themselves easily without tending and form an animal protection layer.
even when i put stuff in pots and containers, i put blackberry canes around and over them sometimes, or let the blackberries grow over them and it works really well to protect them. young trees actually like the bit of shade they make too, especially in this hot dry climate.