I am late to this party but, first, Lori your photos (both) are beautiful, and second, I am all for defense gardening. Nothing like a thorn bush or densely packed pine trees to build your perimeter with style.
I helped a friend plant yucca plants at the beach. They have pointed leaves to keep neighbors' dogs out of her yard. They require no maintenance or watering. You can harvest sprouts off the main plant and replant them easily.