Bambo is a very good idea. It looks like something that just happened to grow there but it requires a lot of effort to penetrate.I've been thinking of planting bamboo along my property line as a natural barrier. Grows like a weed & you'll notice if someone's trying to chop them down to get through. If you dig up a 3ft wide area and line the sides it will stay contained & just grow thicker without any encroaching on your property.
This way you won't have people peeking over your fence to see any garden you might be growing.