I have always thought that if I moved every 10 days or so, then the campground would not think that I am trying to max out the 14 day rule.
The 14 day rule is there to prevent people from occupying all the sites while they spend the summer working near a park. It is also there to allow campers to visit during the weekends, and not come to a park that is sold out. When you arrive and plan on staying 13 - 14 days, it will send up a red flag to make sure you do not look like a squatter, but are real campers just visiting the area.
Keep the campsite looking decent, and you really never should have a problem.
Fred.