I have two dogs that have never bothered my chickens or the coop until recently. Neither of them bother the girls, but my boxer/lab has gotten into the habit of climbing into the coop and getting their eggs. I'm not happy about him getting the eggs, but am really not happy about how he is breaking the coop. I've given thought to taking out the ramp. Will the girls still go in and out when they need to lay or go to roost? It's winter here, so hate to risk them not being able to get out of the cold when they need to. Any suggestions on a barrier that will allow my girls to wander free, be able to get in and out of their coop, but to keep the dog out?
I saw a design someone made to keep their goat out of the coop. It might work in your situation. they basically made a baffle over the pop door which the chickens had to duck under to get in the door. the goat, being much bigger couldn't do the same.
Do you have a smaller pop-door for the chickens to go in and out of? How high off the ground is their door? Is it a raised coop? Can you make the opening small enough for the chickens, but too small for the dog to get through? My chickens have a pop door on the side of the coop that leads to their attached run. (Until recently, the run has been left open for them to free range, but we are currently experiencing coyote problems) The door is about a foot or so off the ground and they just hop up. Maybe you could post a picture of your setup so others can offer suggestions?