We have always given our dog all the food he wants, whenever he wants it. I often fill a bowl that would last a week or more before I would need to refill it. In the last 6 years (he is 9 now) his weight has not fluctuated more than 1lb in either direction at his annual checkups (I should be so lucky!). Sometimes he goes 3-4 days without eating anything, and then suddenly he goes in and devours the whole bowl. Other times he nibbles a little each day (always just before bed). I'd like to think we were smart enough to have planned it this way, but my guess is that some dogs, like some people, have a harder/easier time controlling their weight. I think what helps him is that we have a lot of land, and no roads close to the house, so he gets all the exercise he wants everyday.