If my dogs are gassy, to me that means that their food is not aggreeing with them. Here and there, fine, that's pretty normal, but constant and really stinky? I'd find something else to feed.
That said, sometimes if a dog gets a lot of exercise and are hot, they can get pretty gassy I've noticed. That happens to Ripley if he's ran around a lot in a day, and it's not a diet issue in his case.