Though this is basically taking an idea from StarHunter 2300, I think it would be interesting if there were bounty hunters to help as a payable defense. They could cost less than the pirates and be on call rather than on a ten minute time limit. They wouldn't have as large a fleet as the pirates, but perhaps they could have more diversity in fleet depending on affordibility. Such as the least expensive bounty hunters would have frigates, more expensive would have crusiers, and the most expensive would have capital ships. Perhaps bounty hunters would be the wrong word, but basically these would be mercenary defenders, perhaps at a lower cost than buying the actual ships though these would only be in service for a limited amount of time.