We have a ShihTzu who herds/protects our flock here in the backyard. We currently have five pullets, and one cockeral (Buff Orpington).
And out at our farm we put the seven Australorp pullets, and two of the Buff Orpington cockerals.
They are all tame, but we kept the most tame rooster, and all the female Buff Orps because we wanted to have purebreds.
But yeah, my ShihTzu does a good job at protecting, mingling, gaurding, and herding my flock. They love him, and he loves them. They have grown up with him since the fourth day of their lives!
They are used to having their butts smelled, and having their "group" be seperated by Benji (that's my ShihTzus name) walking through, and having Benji lay down next to them, and what not.