Sure wish we could plant some bait plants, stake out your house (with a pot of coffee to stay awake) and catch them red-handed. Maybe bait with plastic plants, go the old crazy lady way and plant fake silk flowers except with lines attached back to the fence, hidden by mulch. Add flood lamp and siren triggered by someone pulling at a plant attached to the line, and you can wake all the neighbors up at the same time!
Just thinking wild & crazy, it's so maddening.
Anyone you are a little suspicious of?