Custom made EW ships. The sensors on my ships have a range of 15, they're lightly armed, and they're fast.
Even so, I'll generally have to take back a few worlds, but the Korath will lose 60 spore ships doing it.
'2) Have a tiny ship with one weapon in orbit of each planet. '
I've come across armed spore ships in my games, so this tactic doesn't always work. One had an attack strength of 51.