you could train most herding breeds to herd in your chickens. Even many non-herding breeds can learn to do it. Ducks are a common "intro to herding" animal used to train young dogs.
However, while many dogs will naturally scare off predators, most are not bred with the temperament to put up a fight. You would need a more traditional LGD breed for that and they don't always do well on small hobby farms with only chickens.
Have you taken your current dog to herding classes? While such instincts are easily lost when you don't use selective breeding, almost any active dog with prey drive can be taught the simple act of rounding up chickens with human direction, regardless of breed. If you are wanting a dog to round them up without human direction, it's likely to be a recipe for disaster. Herding is very much a human construct - directed prey drive. You control the dog's desire to chase the running animals. Without that human control stepping in, dogs easily slip into pure "chase" mode, especially with small flightly animals like poultry. Add in how easily a chicken can be killed by simply being stepped on by a dog (even more one big enough to fight off predators). Also, that desire to chase and make the animals run and scream is a self-rewarding behavior. The dog gets caught up in the game more than the job you actually intended.