The Neighbor's Dog

Just one of our dogs, Tasha, as a puppy- 
Our town has an ordinance requiring a 5 acre minimum on land parcels. Many people erect fences to contain livestock. Most people put up deer fencing to enclose gardens, and to protect young trees. A few (especially those who venture up only on weekends and vacations) fence to keep their usually empty homes safe.
My husband and I choose to have no fencing, other than the animal pen and chicken coop which came with the property. Both are empty. We enjoy seeing deer, rabbits, foxes, coyote, and even that mountain lion previously mentioned.
The only unwanted visitor (aside from the religious fanatics who ignore the NO TRESPASSING sign) is our neighbor's dog Murphy.
We love dogs, and have three of them. They're mutts, a mixture of Rott, Dobie, Shepherd and Great Pyrenees. They're large.
We allow them outside to do their business, take walks and romp with us, or to lay on the deck with supervision.
Murphy, on the other hand, is allowed to roam.
We didn't mind (much) when he ran alongside us, barking, when we passed his house. We didn't complain until he began visiting us, up to 10 times a day, beginning about 6am. His visits set our dogs to barking, not a pleasant sound as there's the three of them.
The neighbors built a pen, which he seems to be inside of less and less.
Murphy's latest trick is to stop in front of one's vehicle, barking, and refuses to move. He pulled this new trick yesterday. The neighbor lady dragged her lazy butt off the porch, having one hell of a time getting him away. Meanwhile, the dog jumps on the driver's side door, leaving several scratches. We just purchased this brand new car last September!
The scratches don't bother me that much. I believe the vehicle one drives isn't a measure of your affluence or penis size. It's purely functional.
What bothers me is the owners. We've heard they're planning on getting rid of the dog, and getting another. If they can't train this poor creature, how do they expect the next one to learn?
So what's our next move? We may not have to make a decision as things have been painfully quiet next door since the incident.
I sure hope we don't hear a new puppy yapping away over there anytime soon.