1. The UNSC has been reverse engineering Covie tech. The most notable example is MJOLNIR derived from Jackal gauntlets. 2. Covie ships self-destruct in case of boarders. 3. Protocol is that Covie ships are never to be taken to colonies because there may be trackers on them the UNSC doesn't know about. 4. Getting to the ships are hard in the first place because of their massive superiority in naval combat.