Let me preface this message by saying I am electrically "challenged". I mounted a transmitter in our garage that controls an invisible fence for pet containment in the back yard. One of the posts on the transmitter is where I am supposed to hook up a ground wire attached to a copper grounding rod buried 3 feet deep. The power cable for the transmitter has 2 prongs on it and plugs into a 3 pronged outlet. Isn't the "third" hole in the outlet a ground itself? Can't I hook up the ground post on the transmitter to the ground on the outlet somehow? Thanks.