I have pens in my fenced in yard. I'm slowly trying to expand them until they take up everything (since I can't afford to just do everything over the full yard all at once). My main fence is 6 foot privacy fence sunk one foot in the ground. Mine is just normal privacy planks, but I have seen "stockade" where they overlap the planks in two layers so you can NOT see through it at all. Maybe you could do your whole yard like that? You could maybe leave enough space for a walkway around the outside just big enough to walk through with a weed-whacker, then you'd have a buffer from your neighbors.