At that age, I would definitely have the dog on a Senior food with lower protein and fat content. There are many good foods out there. Science Diet would NOT be my first choice.
If you keep track of the dog's weight (good post ggreg), you can try the green bean diet (old dog show trick) :-) If the dog is putting on some weight, you feed their normal kibble but replace half with green beans (canned, unsalted, fresh, frozen, etc) until the dog gets back down to the desired weight. Actually, any combination of veggies would probably work.
Now that your dog is at the correct weight, you can feed him whatever was his favorite food before, only either increase his activity level and/or reduce the amount of food that is recommended or that you used to give. Anytime we need a dog to lose weight, for example, we reduce by just 1/4 cup his usual amount, it's the easiest thing to do, and then when they reach an ideal weight, we change the amount decreased and move it up, so for example we'd go from 1/4 less to just 1/8 less.
We used to keep a chart on our dogs, taped inside the cabinet where their food is kept, and whenever they are in their first two years, we would do various graphs and measures on the paper, and make sure they're getting enough food and also finding that plateau where their weight is just right. But as dogs get older, they really can't get around as well, so their food then needs to be decreased a little, is all. Chart it so they DO get enough to eat but don't lose any further weight.
You can also try buying Senior dog food, diff brands have those choices, some formulas take into consideration the lower activity level, and thus there won't be quite as much fat or carbs, altho a dog does need more fat than people do, I forget the recommended amount, but there are various lists you can find in books and online that tell you suggested measures of vits, minerals, fat, and so forth depending on the age of the dog, in case you want to make sure that a Senior food has got enough essential nutrients and yet will prevent any weight gain from giving them the bag's recommended amount to eat. By the way, most dog foods recommend WAY more than the dog needs.