As far as we know the only way to keep people off our claimed islands is either by staying at said island and fending off whoever invades, or have mortars on the island to sink nearby ships. Unfortunately players have made the island mortars obsolete by just parking their ship out of range and swimming to the island. And most of the time we’re too far away from our islands to protect it from other clans, so that’s where Hire-able Island Mercenaries make an appearance!
Similar to how we put castaways on our island to work the shop stalls, there would be a barracks of some sort (different from the defense structure) that would house ground troops to fend off potential invaders of your island. Depending on the level of the barracks the npc’s strength would vary in level and power. On another note, what are troops without a commander of some kind? Depending on our reputation we can hire Criminals or Hero’s (perhaps our rivals) to command our island troops thus giving them a sort of army like structure. Also there could be an option to spread out our forces on the island to cover different areas of importance.
The reason why I’m suggesting this is because our current means of protecting our islands are sometimes not enough, and having a npc presence other than our shopworkers would make keeping our islands way easier and engaging.
On some instances this might cause a bit of discourse since Island Claiming is kind of a PvP setting, but not everyone has the PvP skills required to successfully protect their land. So having a few npc’s help you could balance things out on most fronts.