What worked in the body could work elsewhere, which is why phyles had 
their own immune systems now. The impregnable-shield paradigm didn't work at 
the nano level; one needed to hack the mean free path. A well-defended clave 
was surrounded by an aerial buffer zone infested with 
immunocules—microscopic aerostats designed to seek and destroy invaders. 
In the case of Atlantis/Shanghai this zone was never shallower than twenty 
kilometers. The innermost ring was a greenbelt lying on both sides of the dog 
pod grid, and the outer ring was called the Leased Territories.