Well, since he is your subordinate, it will be very easy for you. However, there is nothing wrong with being overs mart if he is okey with you and doesn't pose any harm. In fact many over smart people are usually very efficient. So in a way its better for you and your company. However, the best way to handle such a person would be to make him believe that you know quiet a lot about your profession and he should consult you before taking any actions or making any plans.
Is this a person who feels the need to "prove" his intelligence? If this person feels challenging, I would suggest you publicly acknowledge and utilize his (or her?) knowledge by providing challenging assignments in his areas of expertise, and therefore guide how he applies and contributes his knowledge. The need to "prove" his intelligence will be mitigated when, with your guidance, it can be appropriately used and benefit your department or group. You might assign project lead roles in his areas of expertise,for example, and be clear about when it is appropriate to collaborate on decision making, etc., and how you would like to be informed of progress, actions, etc. This way the person can be acknowledged for the value he brings, and you get the privilege of guiding his further development. Who knows, this person may be of great service to you, and will also likely be glad for the opportunities you gave him. Good luck.
