Rooster and geese protecting against a coyote is a joke. I do not have any Emu but considering they are prey animals I can't imagine them doing much at all to stop a coyote.the last thing you want to "protect" your flock is a predator. trust me, out of personal experience, dogs will betray you and kill your flock when your not looking. instead, try enlisting a goose, rooster, or emu to protect your flock. they are usuly large enough and determined enough to scare off anything, and they wont hurt your flock at all
Also, just because you could not train a dog to protect your flock does not mean others can't.
I have a GSD who lets my doves sleep on her, she is in my room with a open brooder of chicks and one with ducklings unsupervised for several hours a day. She shares her food with the chickens and lays around with them outside.