I'm just getting the hang of the different races and one thing that has hit me more than once is a planet where the allegiance level has slowly dropped to critical levels.  What's the best way for each race to maintain control of their planets?

For example, when playing as Advent, I've made sure that I've explored the planet, increased the population level to the top for the planet, added emergency facilities and then added all of the protective orbiting platforms necassary to protec the planet while I go after the next link.

For 80% or so of my held planets, theis is all that I need to keep the allegiance above 70%.  For some, however, the number just continues to drop no matter what I do.

Thanks for any tips.