Wingnut
As a lifelong resident of Michigan, I can assure you this is not native behavior./w3tcompact/icons/frown.gif This inconsiderate SOB must be from an area in one of our states where common sense was probably shunned in his upbringing. I've been following this thread, and have looked at all the suggestions for extracting vengeance (some quite creative and amusing I might add). But when all is said and done, this is your neighbor. For the time being you have to live next door to him, and to create animosity with him would only lead to more of the same.
Best bet is to go have a talk with him, and tell him, diplomatically, your concerns for the well being of your animals should they be hit by or ingest one of these golfballs. If this fails, then you have every right to go to plan "B" (total vengeance)/w3tcompact/icons/hmm.gif
Let me add, "Welcome to Michigan" /w3tcompact/icons/smile.gif. May your stay here be pleasant and prosperous.