It's great that you have a secure run, I did not notice that in the pics. 12x12 is too small for 12 full grown chickens for full time, however, if they get a lot of time out in the yard, you can probably get away with it. It can take some time to figure out if your dogs will be ok with the chickens. My dog has a strong prey drive, he will kill and eat squirrels but he is ok with the chickens after 2 years exposure and some training. If your dogs have a strong obedience background, it would help a lot. I started my dog by letting him go up to the pen and look at them, called him to me and REWARD WELL for coming away from them, repeat. Let the dog learn that leaving the chickens is way better than staring at them. The chickens also become boring after lots of time. I would never leave the dogs loose with the chickens until you are positive you can call them away, and start with them on leash. Be aware pack behavior can change the dynamic greatly, one dog that might be fine with the chickens by himself, will join in the chase if another dog starts it. If you invest in a game camera, it will help you figure out what comes around, and you can better evaluate the risks of leaving them out in the yard w/o you there. My only daytime predators are an occasional hawk, I do let my girls roam a fenced backyard in the burbs, without watching them. I accept that I may lose one or more to hawks, but I've balanced the low risk with the benefit to the hens. That's what you'll have to do too, or greatly increase your run size, or both. 10 sq. ft per hen is generally considered minimum.