Planetary defenses

OK I've noticed that many people on this list seem to assume that
orbital strikes, ortillery and woning orbit means it's pretty much all
over for a planet, that it might as well roll over and die.

I'd like to throw it back at everyone and ask, if you had to design a
planetary defense to counter such a situation what could be done? How
effective would be ground based wepons? Obviously they could be very
effective against atmospheric craft but what about Stuff in space?

I know fixed defenses may be a problem but what about underground
defense complexes connected by hundreds of kilometer of underground rail
where heavy weapons fuel with the vast power reserves available to a
planet could pop up shoot and scoot? Any ideas? I'm thinking about
defensing the planet here not subjugating it.

Los