For the grounding rod, resistance should be as much as possible low. you have to take care of this two points.
If you install the lightning arrestor outdoors, use the supplied ground lug and a heavy wire (#6 solid copper) to connect it to a good earth ground, such as a ground rod. The connection should be as short as possible.
If you install the lightning arrestor indoors, place the wireless LAN device near a good source of ground, such as structural steel or the ground on an electrical panel. Ground the lightning arrestor by using a heavy wire (#6 solid copper) and connect the ground wire to a good ground on the structural steel or electrical panel. The connection should be as short as possible.