Re: Planetary defenses

As far as genre specific planetary defenses go, some friends of mine and
I were running an abortive space campaign based on the W40K universe. 
Eldar planets were defended not by planetary screens but by planetary
Holo fields (a 40K system that creates a spray of confusing images and
patterns around a vehicle or figure).  Most of the other planetary
defense weapons were at least slightly mobile, and the really big ones
were heavily camoflaged.  The Holo Field made it difficult to spot
launch points and energy batteries when they fired.  We decided it was
created by an ionospheric effect similar to some of the wilder rumors
about the USAF Harp project up in Alaska.

Admittedly, this may not be very useful when dealing with FT, but don't
limit your imagination when you're dealing with this kind of stuff. :)