The grounding rod that connects the home grounding system into the earth is a long metal rod, usually copper bonded to steel, galvanized iron, or stainless steel.
Ground rods come in both 8-foot and 10-foot lengths, with 8-foot being the most common size used in residential installations. As a rule, ground rods must be a minimum of eight feet long and should not be cut down. In very dry ground, which provides more resistance than moist soil (meaning it does not accept electricity as readily), ground rods are sometimes stacked and joined with a special clamp so they can extend deeper into the earth.
Another option is to add a second ground rod. This is usually a better option, but the rods must be at least six feet apart, according to the NEC. Whenever possible, ground rods should go into moist soil around your home. Usually, the area close to the foundation has enough moisture due to runoff water from downspouts.
It is unwise and unsafe to install the shorter, 4-foot ground rods often sold for grounding things like TV antennas and other individual devices. These are not legal for grounding the home electrical service, and they can cause your grounding system to fail when it is needed most.