With coyotes running around, I'd definitely get the guineas into the coop every night. If you train them, they'll (mostly) come back to it at dusk. Some evenings mine seem to be reluctant to go in themselves, and I "herd" them in. Once predators have learned that you have dinner, they'll come back night after night. Guineas are blind at night, so make sure you round them up at dusk if they haven't gone back to the coop themselves, that is if you plan to free-range. If not, then "never mind". Although I wonder if a coyote can breach a fence...dunno. Someone else may have experience with that.
Is your dog trustworthy with the guineas? If you haven't checked that out, you might want to do so. If trained to not eat chickens or guineas, dogs can be great defenders against predators, but dogs are on the predator list - even your own if not trained.