To prevent capture, you'd also have to either ban intel entirely, or make the monster race in such a way that they don't have planets.
Otherwise, there'll be a planet path, and they will be vulnerable to CI/PPP. (And CI applying to, oh, a giant space squid is just...
weird.
) If you give them powerful intel to defend, they'll probably also use that to attack -- which is also rather odd.
------------------
-- The thing that goes bump in the night