24
10ft tall all down the driveway, so the potential new neighbors can't sit there and creep on me on their porch while i'm watering my plants in the drive, and as a bonus it'll keep their tree's stupid leaves in their yard where they belong
you can't even say i'm becoming a suburbanite, the town i live in is rural 
I think a 7-8 foot fence would work well enough for this specific case, it's just our main entrance is on the side of the house with a driveway running along it, and their front door and porch are like 20ft away. I think at that distance i'd feel obscured enough doing stuff in my driveway
I could also just get over my desire to not be perceived