[gravey101]

I usually ignore plaentary defences altogether, other than a few mines in the early game. Defend the warp points, where you always get first shot. If the enemy gets in your systems you are in trouble. I have never seen planetary defences able to stop a decent fleet. For warp point static defences I will use some mines again, and maybe medium sized satellites. Generally though I figure that I would prefer to invest my resouces into mobile, upgradeable weapons. I.e. Ships. The zero-maintenance of units of nice of course, but as a general strategy I find offence to be the best form of defence. Get in the other guys systems first. If you sit there and wait for him to come to you, you will likely be in trouble when he does.