Here in Philly, we find it really helps that there are people living all around the garden to watch, call cops or garden coordinator or just yell a lot. It also helps to share produce with non-gardening neighbors. We've been known to shame people who steal collards by yanking the whole plant by telling them very loudly that they're so dumb they don't even know how to steal collards, and explaining, also very loudly, that they should only pick the leaves and leave the plants. Benches in the shade where older folks and folk who aren't working can just sit and gab keep the place occupied and of less interest to vandals. Involving neighborhood kids, who are probably doing most of the vandalism, in the garden or its projects can be helpful.
Night lights help.
Rumors of TV cameras help a lot. My garden must be n-dimensional if it's out here in cyberspace.