Tzeentch laughs at likely
Join Date: Dec 2009
Location: Inside my Head, Bristol, UK
Harrying around a unit like that is one of the things Fast Cavalry are good at.
The counterbalance is that the FC unit is usually paying for the privilege in points and it doesn't work very well if your opponent supports his units with other units.
The only way to beat it with a single unit I can think of is if the attacked unit managed to get Random Movement; then they could turn to face and wander into melee.