Ok I just figured out how to get this achievement EASY. I was playing around and figured out a way he would miss you 99% of the time . A friend and I just got this in 2 minutes. There are 3 main things you need to know to do this.
A. MUST HAVE THE Seal of the Scout. (allows you to dodge without fatigue.)
B. HE MUST BE ON YOU THE WHOLE TIME! (kill all the bots helps)
C. It is the attack that that he swings over his head at you.
When he is on you get close to him and hold block. You want to be around sword length it seems or maybe a little farther. Hold your left stick in the direction you want to go and SLIGHTLY hold the right stick so you are straifing (i held left stick right and the right stick sligly left). While doing this repetetly tap the A button to jump and it will cause you to dodge over and over and u will be dodging a circle around him.
If i can figure out how to post a video here from xbox i will record myself doing it if that helps anyone.
Feel free to msg me in game if you need assistance.
P.S. This achievement pops as soon as you get enough dodges, you do not have to finish the mission!!