The rod must be at least 8 feet in the ground, and should be below or flush with the ground level. If the electrode is above the ground, it has to be protected from physical damage.
So if the rod is 8 feet in the ground, you'll simply have to protect the aboveground portion from physical damage.
National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 250 Grounding and Bonding
250.53 Grounding Electrode System Installation.
(G) Rod and Pipe Elecgtrodes. The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil. It shall be driven to a depth of not less than 2.44 m (8 ft)... The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10.
250.10 Protection of Ground Clamps and Fittings. Ground clamps or other fittings exposed to physical damage shall be enclosed in metal, wood, or equivalent protective covering.