FWIW my roo just saved the flock from a red tailed hawk the other day, sustaining some lost feathers and a cut on the comb. After the hawk left, he huddled them all under a dense pieris. It was just a little before sundown and I watched him very carefully move the flock closer to the coop and then get them all in before going in himself. So far, he is the best roo I've had -- a 9 month old EE.
That said, I don't count on him to protect them all the time. They've since been locked in the run because the red tailed hawks are a nesting pair nearby

Also, I only have 6 hens -- 24 would be a lot for one roo to wrangle in case of a predator and it'll take time for them to all bond and move as a flock as some assertive hens will surely try to reject him.
I don't have experience with roosters and small dogs but an old roo of mine -- also a very good boy -- went after my large-ish cat a few times as she tried to sit with me in the coop. Certainly taught her to never go near the chickens, though she is the biggest wuss ever and didn't really need to 'learn' that lol. Like someone above said, it depends on the dogs and the roosters. My mom has a doxie mix who is spoiled and basically feral. I can totally see that dog getting pecked and then ripping the roo to shreds. Similarly, I have a pit/basenji who has never been pecked and remains very wary of the birds even after 4+ years of chicken exposure. I have an Aussie/Catahoula, also, and use a training collar on her that can shock, beep, and vibrate. I mostly use it for trail running and when they ride with me but it was also helpful with chicken introductions, especially as she doesn't see baby chickens as the same as grown ones and thought they were super fun to try chase (through the fence). I almost never have to shock her, she responds just as well to the vibrate.
So, tl;dr: it depends on the roo and dog, and you might need to be aggressive with your dog training.