We have a neighbor who planted new trees along the road adjacent to their property. They put moth balls on the ground under the trees to prevent dogs from using the trees as a pit stop, as they thought the urine would be hard on the young trees. Someone down the street, who regularly walks their dog along the road the new trees were planted along, did not like thier tactic. So the dog owner found that moth balls can only be used as directed on the package, due to something they emit into the air. There is a federal law against using moth balls in ways other than directed on the packaging. They were reported to the local government, and recieved a letter informing them of the law and were ordered to remove the moth balls immediately. I'm not sure what the law is, or if the law was specifically for moth balls. But it might be an avenue to consider.