I learned the hard way. Not with my current flock.MIne either, I am fortunate enough that there is enough space that they are 100% apart unless the dog is with me and goes into the chicken yard, then he is met with the coop and run. So they know each other, see but no touch.
The dog only weighs 12 pounds and I think the 15 hens would not put up with any nonsense from him. but like I said, no reason to find out.