Don't think there are no coyotes in your neighborhood just because you haven't seen or heard them...they can be found in every state and in cities (L.A., St. Louis, Denver, Chicago, etc.) and the country. Coyotes live very well and raise youngsters successfully in urban and suburban neighborhoods and breed with domesticated dogs (if they don't eat them first).
As for dogs Many, if not most dog owners will let their family dog out before dawn to roam and do their "business" somewhere other than their own yard...and they will pack up and roam through their neighborhoods like a bunch of young thugs looking to boost cars and make trouble. They are capable of demolishing your flock for fun before going home to see what's for breakfast. They'll climb through chicken wire like it wasn't there and dig under any fence to get them.
You also have to consider predators with wings...hawks, owls, falcons, roadrunners, etc...all hunters who find chicken very yummy. And snakes of all kinds that will find the smallest hole to sqeeze through to eat the eggs.
You don't need a totally enclosed coop but your yard has to be well built from the roof to below ground level and all doors and gates must keep all the above mentioned creatures out. Your chickens need sufficent room to get out of the rain, mud puddles and wind (even dry wind)...they don't like their feathers ruffled while roosting, that is for them to do to themselves, thank you! And if they don't feel safe, secure and private in the nest box they won't use them.
I envy you for living in an area where the weather allows a nice open coop...suficent ventilation is almost everyone's biggest concern.
Just build it like Fort Knox and both you and your chickens will sleep well at night.
