Again, this isn't directly related to bounty boards. It's not possible to fully cover defense simply with bounty boards, even if the owners are an official faction.
The whole point is to have a system that gives defenders the same rights as attackers. That cannot and should not be done with bounty boards alone. The system is supposed to allow defenders to attack base attackers they would not be able to otherwise, by doing relevant RP and declaring it, just like the base attackers.
Bounty Boards do not give engagement privileges, except to the BHG and Freelancer ID. Nor is the Bounty Board system necessarily appropriate in roleplay for this sort thing.
How would it not be possible to cover this with bounty boards? A example Kruger has almost all unlawfulls bountied on our bounty board. I am convinced a lot other factions have the same in other area's of the game.
If you are unable to defend your station in a system then you should not be there with your station and IFF in the first place. It would mean you operate outside of your ZOI.