We have a beagle that we trained with the baby chicks. We kept them in the bathtub because it was too cold to be outside yet and invited him to see them with us. We would hold them firmly and let them smell them. He would lay down and roll over expecting a "treat"!
But we kept training him and told him "NO! MOMMY's!" Then I would hug them and love them to show him they were mine. We would also praise him and give him affection when he would just smell or stay still when we put them close to his face.
He constantly pined for them and we keep training him as they grew. We always kept them separate in a fenced area and under supervision.
And then, one day, they were big and they PECKED HIM IN THE NOSE whenever he tried to smell them! He never bothered them after that.
That was our first flock. We have a new flock of 11 week olds now, and he doesn't bother them a bit. We are in between run styles right now, and he was even able to dig under the temporary fence and get in with them. All he wanted was their yummy kitchen scraps. The cute/wonderful thing was that Anastasia, one of our older girls who ranges freely through the yard, stood outside the run squawking her head off to let me know Sherlock was being naughty!
We have 2 cats that don't bother them either. One couldn't care less and pays no attention whatsoever. The other cat is a mouser and defender. She was out tonight chasing off the feral cat from next door when we went out to close up the coop. She often hangs out in the coop with them waiting for mice to pop out. We've had chickens for 2 years and she's never harmed any of them.