Originally Posted by Valgor
Instead of a stationary fleet of defenders, planets could have armed satellites in orbit, equipped with shields and weaponry determined by the colonizing race's tech level.
According to some other posts it's already too easy to bomb planets due to the defending ships staying at the planet as long as you don't attack it directly. These satellites would need to have a higher range than the players bomb range, and I don't know how big that is. An alternative would be to have star bases which can launch fighters.
OP: I think this would be a great idea. It would add a lot to the feeling of a living galaxy!