My 4 yr. old BC, Dakota, has been herding a soccer ball back to my feet since he was 8 mo.'s old. Now with a new 6 mo. old BC, Aspen, at home she chases him and nips at him when he starts to herd the ball and he stops. Any suggestions? He will still herd it back to your feet as long as she is restrained but I hate to exclude her. Thanks