Lesley,
Very sorry to here that you have such barbarians in your area. At our Sacramento garden we have to put up with such things too. A few years ago, I strolled to the front yard with a hot morning tea to find someone in the front yard with an arm load of our flowers ripped from the ground. When I was noticed, they jumped away like wild deer smashing more of the garden before jumping in their car and speeding away. We are not the only ones having to put up with such nonsense in our area. Most of our gardening goes on in the back yard now.