Growing Berberis darwinii under your windows should be enough to deter most opportunist thieves from entering your home – the thorny stems and mini-holly-like leaves are viscious! This is also an attractive plant, with glossy evergreen foliage that sometimes turns red in the cold and bright ornage flowers in May – here it contrasts beautifully with the purple honesty (Lunaria annua) that self-seeds around my garden every year.