Currently, the NPC factions often have difficulty defending their non-military worlds. Frequently, the only obstacle to raiding a planet is the local station. Similarly, players are well advised to have a military base on each planet. There is some overlap in patrols, but it is strictly infrasystem and is often not consistent. Planets can receive resources from other same-faction planets, but defense is highly localized.
To resolve this, I propose a dedicated interplanetary and intersystem patrol system similar to the existing trade fleet system. Each faction would evaluate the defensive posture of their planets and allocate fleets from their bases accordingly, with each level of base having more fleets and greater range. For instance, Coatl might deploy rotations fleets to ensure Chicomoztoc always has a defense force in orbit. Similarly, Jangala might deploy fleets to patrol the Galatia system.
This concept could be further expanded to integrate with the trade fleet system. If all markets have sufficient protection, a faction could send fleets to patrol key trade routes for pirates. e.g. A player waiting to ambush a trade fleet might be found by a Hegemony patrol and asked why they are hiding along the planned route of a large trade fleet.