God I wouldn't wish to be a shepherd IRL after playing this top-of-the-line simulation :D Maybe making the sheep more predictable and having some gates at the entrance to prevent the already stored sheeps from running away would make it a bit mrore forgiving to the players.
Also each sheep being somehow visually (and maybe a bit mechanically) different would be a nice little touch, so you could shout "COME ON BECKY, GET BACK TO THE BARN" while getting that one sheep out of the corner :D