Ordinarily, moving in next door to someone you're looking for dirt on would be considered over the line, even for a soi-disant journalist. One might even go so far as to call it "stalking."
Unless the person has been so insolent as to run for public office against The One™. Then it's perfectly justified and her own fault. Stop being such a crybaby! Who wants to see your teenage daughters naked anyway? Get over yourself, lady!
Unfortunately, if he stays on his rented property and simply spies on them, she doesn't have any legal right to part his hair with a shotgun. And with guys like that, restraining orders just make them laugh and take twice as many photos. All we can hope for is that he tries to slip into the house.
And yet journalists insist on calling what they do a "profession."
Update: I like Darleen's idea:
Besides a fence, I would suggest the Palins set up a website with a live feed from a couple of cameras trained on McGinniss’s summer home.
Let the public watch the watcher.