wabbit... most california municipalities require that barbed wire tops be canted inward to prevent injury to those passing by outside the property, particularly if the fence borders the property line.
this is a frequent canard used by the "FEMA Camp" nutbars to "prove" that railway turnarounds and service yards, bottling plants and undeveloped county parks are actually concentration camps.
for nearly a decade camarillo state mental hospital had a cyclone fence with an inward canted barbed wire topper on it's north side. this was to keep the critters out, not to keep patients in, since the fence only went along the frontage of South Lewis Road, and stopped immediately where the hospital property ended, leaving sod fields, a mushroom farm and a 3 inch deep stream as the remainder of the "Barrier' to keep the kludges from escaping. thats right, a 6 foot cyclone fence with inward facing barbed wire toppers on ONE SIDE of the property. no fence on the remaining sides. why you might ask, would you build 200 yards of fence on a property that spreads across nearly 4000 acres? it creates the impression that the hospital is secure to discourage casual trespassers and gawkers from bothering the loonies. why was the barbed wire canted inward? because tall people (like me), people on horseback, and agricultiural vehicles kept hitting the barbed wire topper when it faced out. somebody had the brilliant idea to turn it in, and it worked. most new fences in california are REQUIRED to have their toppers turned in.
you also may not construct your house in such a manner that the 2nd 3rd 4th and 5th floors extend over your neighbor's property.
just cuz it aint toucching their dirt doesnt mean you can build over somebody else's head.