He was eager to help.
And no more rat!
Now helpfully he doesn't do that to the chickens when we get some...
Sounds like your new dog has found a way to earn his keep, Wade.
We've had all kinds of dog personalities in our lifetime and the best ones came from a shelter. Sometimes a dog can be trained to guard chickens. Sometimes not if the dog is a natural hunter: those tend to go after the chickens too. We just kept the chicken run well fenced. We took a section of sturdy wire fencing and connected it tightly to the upright fencing and had it laid on the ground and anchored. It's like an L
with the leg of the L outside the perimeter. This deters dogs, coyotes, raccoons and many other predators from digging under the fence and getting into the chicken run. The run had fencing over the top to keep predators from climbing over the fence too.
A well built run keeps out predators for years. The one that's on the farm now is made of chain link fencing and it's been there 22 years. It used to be a large dog kennel and the new owners of a home in town gave it to us for free because they're cat people, not dog people.
We also attached tightly woven hardware wire inside the lower half of the pen fence to keep the chicks from wandering through the chain link.