When I help my clients with landscape design and maintenance, security is often a big issue. While open designs and low metal fences can be attractive, they don’t always keep unwanted visitors at bay. And to keep children safely out of swimming pools, we need to secure our spaces properly.

I was at my dentist and noticed such pretty plantings in the parking and entry areas. I asked who did their gardening. “Pam, who is a co-owner of the building. Aren’t they sparkly and cheerful?” said my epic dentist, Dr. Wendy Wakai. “But we have such a problem with people hopping the tall wall … even though we have security cameras.” Auwe.

After my appointment I went and admired the flowers, rosemary, succulents and other plantings. The wall was about 8 feet tall. I envisioned a landscape design that would artfully and effectively help prevent future invasions.

Some plants with thorns would work. Super-thick hedges can also deter trespassing. Motion lights and even motion-­sensing irrigation that comes on full blast when people trespass, are some green industry technologies that can be employed.

A few plants come to mind that could quickly become a thorn in an intruder’s side:

>> Carissa, or Natal plum, has wicked thorns and can grow quite dense with time, good horticulture and proper selective pruning. It’s salt tolerant too, as many local gardens are on or near the beach. The trick is finding big enough ones in the landscape nursery.

Bonus: Carissa shrubs have pretty white, fragrant flowers and will produce a red edible fruit. (I’m a firm believer in useful, multipurpose plants in the garden.)

>> Bougainvillea is also nice and thorny and can grow thick quickly. The plants provide gorgeous flowers in the landscape and for lei making. However, they don’t like salt air on their leaves. So if it’s a coastal area, or if there are salty Kona winds, you’ll need to rinse off the leaves.

>> Hala, or Pandanus, is a native Hawaiian plant and a canoe plant, carried here by akamai ancient sailors for its many uses. I love them for their beauty and thick, dense thorniness in a landscape. They love salty air, or ehu kai. In fact, if you ask lau hala crafters, they will tell you the best lau or leaves are from young, coastally grown trees in maximum windy, salty air.

>> Dragon fruit is another winner, especially for topping a wall. They like to grow up a wall, or even on a strong chain-link fence. And they’ve got some mean sharp thorns. I was dealing with some cuttings recently and had to remember to put on my strong gloves. They too have gorgeous flowers and will produce yummy, nutritious fruit. Pro tip: Hand-pollinating gives you more fruit.

There are also lots of thorny palms to choose from. If a palm has thorns, it tells you that it is not a native plant. (Our native loulu palm trees have no thorns.) But palms that evolved with hungry grazing ungulates do have thorns and can also be strategically planted to repel and deter intruders.

Heidi Bornhorst is a sustainable landscape consultant specializing in native, xeric and edible gardens. Reach her at heidibornhorst@gmail.com.