"Weasels are the only predator small enough to slip between bars and vanish in the night, unseen." Rats, mice, snakes.
Since you didn't put where you live and how much area your coop is on, it's hard to help.
Any dog can be trained and is only as good as it's training by You. But it takes years and sometimes they just kill a hen for fun because they are bored. If this dog has nothing to do for 350 days of the year it will get bored.
Are you talking you live on a farm and want an outside dog? Because really that's really the only thing that will help if it lives with your hens....
I too was looking for a better breed, or I should say asked if others have used a specific breed but all in all any herding dog will do, terriers too. Just know they are usually high strung and need a real Job on a constant basis.
Honestly if you got weasels the only thing is to kill off the weasels.... buy a 22 rifle, practice shooting. It's easier and faster then training a dog.
I'm going to edit as I'm just starting to read some of your answers here and say... you have All those animals on a 1/3 acre lot? Weasels will smell all that and you have easy pickings there. What major metropolitan area allowed all that ? Just curious because if they do then a 22 rifle would not be an issue.
Also you jumped on people quick for no reason. Maybe if your original post listed all the facts instead of a quick summary it would have been a little clearer. But I'm gonna guess I too will be on ignore too.... don't worry I like it there with a few others
P.s., this is a big forum. If you ask a question you will get all sorts of answers and if you choose to ignore people because you dislike their answer you will have a large list and miss out on Very good advise.
Also, there is a search feature here, dogs have been discussed many times before