Earthguard is the name of the small group of Spathi and Ilwrath ships chosen by the Ur-Quan Kzer-Za to keep an eye on the slave shielded Humans, to make sure that they are obeying the imposed restrictions. The Earthguard was stationed on a base on Earth's moon.
The Earthguard fell apart when the Ilwrath ships were recalled on a command of what the Ilwrath believed to be their gods Dogar and Kazon. Without the Ilwrath's reassurances, the remaining Spathi contingent gave into their fears that the Humans would try something sneaky. Accordingly, they made a series "strategic redeployments", moving the entire group to Mars, then to Ganymede, later to Titan, and finally to Pluto. By rigging the Hierarchy Moon Base to still appear active, they effectively kept the Humans from learning about this migration. The Earthguard was further whittled down as Spathi ships one by one returned home, until only Captain Fwiffo in his StarRunner remained.