If you are feeding him a low quality food, this may be part
of him problem....If what he eats is full
of grains, by-products, chemical preservatives, dyes & no real nutrition, you need to adjust to a high quality food...All the grains in most dog foods are very fattening....
Also, you can add fresh veggies to his meals & gradually start cutting back on his food....This will help keep him full w/lower calories....
Be patient & don't give up....