I am glad you brought up the subject about using mothballs outside. It was a practice that we used from time to time when we breached beaver dams many years ago, and due to the location and time year would be determined the amount of success. We found it only to be temporary matter of few days a week at best.
You might be wise to contemplate putting in a pet door with an electric locking device which is tripped by the pets collar. This would alleviate any of the neighbor's pets or wildlife entering your home.
In regards to the mothballs, they are a class of pesticide and depending where you are they could come under federal or municipal laws and/or state or provincial law so it's worth checking into to see where you stand. I'm enclosing the excerpt from a website showing some of the side effects of using mothballs outside.
"The bottom line is if you choose to use mothballs use them responsibly. Donít use them as air fresheners or home remedies. Store and use them properly in the house. Never use them outside to deter snakes, skunks, rabbits or other wildlife. It will not deter them but cause a slow, inhumane death by damage to their liver, kidneys, a breakdown of red blood cells and brain swelling. It can also affect our four legged family members."
Here's the website that the abstract was taken from
As I mentioned I am glad you brought the subject up. I hear other people in the area talking about using mothballs in this fashion. At least now I'll be more informed and be able to warn them of the hazards of mothballs.