It is vital not to have a block of tenure on the Board that is going to cause you a problem at some point.  I look at the tenure of the Board as a typical curve.  You want corporate memory; two or three directors who have been there for a long period, two or three who are relatively new to the board, and the rest in the middle.  In that way, the Board can be gradually and effectively replenished over time.  [From AICD Magazine, May/2013]