I'm wanting to get 4 chickens but would be unable to let them run free in our yard do to a 3.5ft fence that we would not be able to make any taller. I'm not confidant that the chickens wouldn't simply hop it, even with clipped wings, and either unset our neighbors or be eaten by their dogs. If I had a run attached to the coop how big would it have to be to have happy health chickens?