My dog's diets consist of mainly raw chicken. Bones and all. You want to avoid cooked bones of any kind, but the majority of dogs can eat raw bones. The myth that chicken bones are bad for dogs is just that, a myth, unless they're cooked of course. Chicken bones are rubbery and don't splinter. And if your dog chews his food properly he'll be fine.
That said, since my dogs eat raw food, having it available for them at all times would just be gross. LOL. Feeding kibble is a different story. If you feed just dry kibble, there's nothing really wrong with leaving their food out all the time with the provision of a few things. First of all, you want to measure the amount of food you set out everyday, so that you always know how much your dog is eating in a day. This is often the first sign that something is wrong with your dog that might need vet care. Next, your dog needs to be able to regulate himself. Some dogs are natually chow hounds, that is, they eat whatever they can get into. These dogs will just make themselves fat if free fed. Other dogs, some breeds commonly, are self regulators. My dogs, if fed kibble would regulate themselves I think. I know my big dog would, maybe not my little one.
To specifically answer your question, I feed once a day, with small treats throughout.