One of the best ways to keep thieves out is to use the arsenal of defence created by nature evolved over many years in the form of thorny prickly plants. A prickly hedge gives protection all year round, be it on a boundary or close to a property with its seriously unpleasant habit, fierce to push through or try to climb over. Evil thorns, scratching and piercing skin or sharp pointed leaves are often enough to keep burglars and prying eyes at bay whilst being visually appealing to those around.
As well as planting a hedge, perhaps one such as Berberis Stenophylla, known to be one of the prickliest or Holly, there are several other ways of using these barbed plants to great effect as an impenetrable barrier whist capitalizing on the beauty and added benefits to nature of these plants. Instead of trellis on the top of a fence, try running a couple of wires between the posts and train a thorny Rose or the evergreen Pyracantha along them creating a pretty yet extremely good defensive boundary.
If wanting to create a thorny thicket virtually impassable on foot therefore repelling intruders to great effect, plant a dense cover of Gorse or foundation plant roses such as Rugosa especially under windows. Quickthorn also known as Hawthorn, Blackthorn or a Mixed Native Mix are excellent choices of plant to create boundary hedging plants that can be planted on a budget and with patience these develop into dense and secure boundary fences often used by farmers.