With the changes from 1.04, military bases now prevent a planet from being invaded.
This was a great change; one nice thing about this is that now you can just park your fleet on a military base to protect ALL your planets at once.
However, I noticed that when I moved my fleet off my home planet, I got hit with the 10% approval penalty for leaving my people "unprotected."
There should be a change so that either a nearby military base or a nearby ship (like one defending a nearby base) counts as "protection" for citizens.
But perhaps the whole protection mechanic needs to be fixed. It's just silly that right now you the game considers any puny little ship in orbit as "protection." Maybe the penalty could scale according to the level of protection (or lack thereof). Military starbases could add to a planet's "protection level."