I have currently my furst game wit Nomad pklanets. And I had teh situation of having a mark IV Ion Cannon very close to my home planet. I could've destroyed it but Mark IVs are rare and useful, so after some painful raids and pressing to build a command station I got it.
And then I see it. There was still a guard post next to it that I didn't noticed or didn't bother. worse, it was under a force field. I tried to save the Ion cannon but it was too late.
Best part: As soon as I had the pkanet I saved because I was happy that i finally got it. Instead of saving BEFORE I capture it. Ugh, this was so DUMB!
Anyway, for people who want to have a good laugh at me, I added the save.
Next time I will clear everything before taking a Ion Cannon. I thought " I don't need to clean it, the Ion Cannon will take care of the frees ships" and that's exactly what it did. But that does not count for Guard Posts and having one right next to it is very bad.