Lost 3 planets toi enemy intel ops. help!

[Drakish]

I just have the demo but I have a problem. In the Last few turns I have had several planetary rebellions and have lost 3 worlds to an AI empire with whom I'm at war. I have been increasing my intelligents facilities but am still quite far away from the number of points for intel defense level 1 to be paid for each turn (can't remember the name). How can I stop them from doing this and how can I get those planets with the populations back. Do I need troops or intelligents measures or both. This is mighty un-nerving :-(