a fox wouldnt dare attack an adult they are not suicidal i saw a pitbull kill one, an emus kick can do some serious damage but some dogs are too strong. I am not sure about coyotes, they should be fine around but who knows. Domestic animals are always diff from the wild ones. In the wild only the strongest ones survive but in farms we breed the ones we like with the mild manners. So some might not fight they might get scared. I don't think it will get scared of a fox though. To a medium large dog a fox is just like a cat.
A fox would dare to attack one.. I've seen it.. hated to shoot her because I know she had babies she was trying to feed.. but I couldn't have her attacking my emus at night while they were bedded down
a sleeping emu looks like a big goose to a fox.. they smell poultry and don't avoid the emu just because of the size