the biggest risk where chicken poop can make dogs sick is by being eaten, as it can pass salmonella from the chicken to the dog. Salmonella bacteria is shed from the chicken via feces and can then infect the dog once ingested.
How you can stop your dog from eating chicken poop:
Keep the coop and run area secure and clean: As the possible harmful bacteria is in the chicken poop, you need to stop access to the area. The best way to stop diseases being passed between dogs and chickens is to keep their enclosures completely separate, you could also try distracting your dog, keeping him supervised, and obedience training
keep your dog away from chickens and their living coops. Dogs are playful and instinctual, and will do what they will for interaction and sustenance, including eating their fellow animals poop.
You can also engage your dog with exercise to tire them out and keep them focused on you, while obedience training is an option to enhance their listening skills for when you give them a direct order.
Best Regards.