try and surround him.....and also, try and make sure u ahve a lot of FAST cavalry units in your army in reserve when u go against him....then if he tries to leg it, chase him down with them...horse archers work well for this. Also, even if he does escape of the field, u might be able to split your light cavalry from the rest of your army and engage him in a second battle (in which he HAS to fight, if he runs off the field he dies anyway)...u can do this because light cav have the longest campaign map movement in the game.