Your neighbour is perfectly within their rights to put the towels soaked in J's fluid down in the garden. They are also entitled to put gripper rod on their side of the fence. However, who owns the fence, you or them. If it is your fence (you or the previous owner erected and you have responsibility for it's upkeep), you can remove the gripper rod as the fence belongs to you. The real problem lies in the fact that you allow your cats to roam wherever they wish. You complain about your neighbour but just put yourself in their shoes. They might not like cats. I have no objections to cats until they come onto my property and crap in the borders, bury it, only for my wife or I to get it on our hands when gardening. The responsibility is firmly at your door.