Ask Mr. Smarty Plants

Several plants come to mind.

One, Tasajillo, or Pencil Cactus (Opuntia leptocaulis) is a member of the Family Cactaceae (Cactus family). It is shrub-like and grows up to 5 feet high. In the winter it is filled with bright red berries, giving it another of its common names, Christmas cactus. Its many sharp spines and the fact that it tends to form inpenetrable thickets makes it a good deterrent against intruders.

Another plant, Agarita (Mahonia trifoliata) is a member of the Family Berberidaceae (Barberry Family). It is evergreen with holly-shaped leaves. These leaves have stiff spines on their three-pronged tips. It is shrub-like also and grows up to 8 feet tall. In the spring it has fragrant small yellow flowers that produce delicious red berries that are enjoyed by birds and other wildlife. It, too, can form thickets as a barrier.

There are two members of the Family Agavaceae (Century-Plant family) that would meet your criteria. They are Spanish dagger (Yucca treculeana) and Buckley yucca (Yucca constricta). Both have long leaves with sharp spines at the tips and both have attractive flowers that serve as hosts to various butterflies and moths.

You could possibly use all four of these plants in combination to form an attractive and effective barrier.