proper grounding at main service drop panel
If the concrete encased electrode is of at least 20' of bare solid copper wire buried within 2" of the ground in the concrete footing/foundation or is connected to a galvanized pipe of the same length, it is considered a sufficient grounding electrode.  As a side the code allows the re-bar that is encased in the foundation/footing if it is all tied together with standard steel tie wire to serve as the electrode. No additional ground is required.  This is how I read the code. It is always wise to check with your local inspector.