After following a few of the threads regarding defences I just thought I'd chip in with a little idea similar to something in EaW.

Add a garrison or defensive fleet option to planet upgrades or such, limiting it to frigates and not cruisers to provide some kind of mobile defence beyond strike craft from hangars. This would I think help free up fleets to go on the offensive on large and huge maps which I've noticed people saying they end up having their fleets locked up defensively and being unable to move without losing the planet.

(Only played small and medium maps so far but can see the issue when fleet cap has nothing to do with the size of your empire)

Maybe add a seperate category on the planet upgrades or tie it into tactical slots somehow e.g. A planet with 35 tactical slots gets 70 supply worth of ships.

These ships would not be able to join fleets or phase jump from their garrison planet and don't count toward your main fleet supply.

Just thought I would throw this out as an idea and see what people think.