Suggestion - Planet defense systems

With the risk of making the game too defensive and farm oriented, I would still like to open a discussion regarding possibilities to extend strategical options for combat.

You could think of defense systems around a planet that aid in the fleet vs fleet combat around a planet.

Or for instance bunkers(or the already mentioned robots) to aid your population in the invasion phase.

Just a rather generic topic to see what people think about adding defensive options to the mix.