The following rule is still in playtesting.
Single models: it takes 1 action to dismount. The horse is considered to run away immediately. From that moment on, the soldier fights as an infantryman.
As a result of the group order, the player spends 2 actions and places the dismounted troopers in front of the horses and the horse holder in contact with the horses. Dismounted model can then move away freely, while the horse holder cannot move.
If the horse holder is wounded, killed, engaged in hand to hand combat, or if it fails a Morale check, the horses flee immediately.
Mounting is also a result of a Group Order given by a Leader. Spending 2 actions the player gets the reverse result, i.e. all troopers mounted and in base contact. If there are more horses than troopers, the excess horses flee. A horse can never be targeted by enemy attacks (close combat or ranged).