Blackberry brambles are nature's barbed wire. Grows fast and taller than a man when mature, with half-inch thick vines full of thorns. Better than a fence for keeping out trespassers. Also makes for a nice home for all kinds of birds cause the cats can't get at them if they nest in the brambles.

I prefer raspberries desu but blackberry bushes are bigger and meaner. Granted you will have to fight them from taking over your property.