The third hole is a ground however I think that the instructions are asking for an earth ground.

So, what's the difference between an electrical ground and an earth ground?

We installed an electric fence for our dog. I believe an earth ground is running a wire to a grounding rod that is buried in the ground. It was a lot of fun trying to hammer the grounding rod down into the soil, but we were successful. I would install this if the instructions as for it. You can purchase a grounding rod at an electrical supply store.

Be happy it is not a television antenna or you would be driving it 8 feet into the ground. Any metal object on the exterior of your property MUST have its own grounding system independent from the house wiring. Nature is a very funny thing. For some reason it is attacted to bright shiny metallic objects, particularly in a thunderstorm. Why would you want a lightning strike to send thirty gazzillion volts of electricity back into your house? Wouldn't it be better for it to go directly back into the ground like it is used to doing? Start pounding, it's only three feet. Oh, use a copper rod instead of the galvanized.

Ok, thanks for the help. I will be pounding
a copper grounding rod into the ground in the very near future!

Chris.