Planting a variety of Cacti around your home, especially under windows is a great way to not only decorate the exterior of your home but to also help prevent thieves from gaining access to your home.
The sharp points of the cacti make it extremely difficult for someone to gain access to a window on the lower floor of a home.
This can also help to lower home owners insurance as well, depending on the insurance company you are using.
There are other plants as well that can be planted under the windows that will also prevent easy access to windows.
I have seen several homes where bushes have been planted under windows for this reason. However bushes seem to more or less only hide those which are attempting to gain access to someones home. Which is why if this is something that you are wanting to do, should choose a plant which has thorns or spikes like the cacti do.
So when planning on doing something like this to help protect your home, look into these types of plants that will do well in the area that you live in as well as if they need shade or sun.