+1 for airtight container. We had cheaped out on this and just purchased some cheaper plastic Rubbermaid-style containers -- to my wife's horror, she opened it one day to find maggots. She was sicker than the dog ever was (the dog didn't get sick and we threw that container out wholesale, food and all).

We purchased an airtight "food container" with a screw-on lid -- from a major pet store chain, and for some absurd amount of money -- but haven't had an issue sense, and the peace of mind was well worth it for my wife's sake.