The first step is to not follow the feeding instructions on the bag of dog food. Pet food manufacturers will usually recommend 3X the amount they should be given- after all it's their business!

You might try cutting him back to 1.75 cups of dog food per day. Still try to divide it in some way between two feedings. If he looks like he is ready to eat everything in sight, then add something benign like carrots to fill up the tummy. Once the dog is down to the desired weight, try increasing the food intake to 2 cups. If the dog continues to drop weight add more food. If it starts to gain it back, then go between 1.75 and 2 cups. Sooner or later you will find a range where just the addition or subtraction of a very small amount of food will affect the weight. Thus you can alter the amount depending on whether it's summer or winter.

Surprisingly enough I found exercise not to be effective in removing weight from a dog. I would exercise mine until I was exhausted, and she would ask for more exercise losing no weight in the process. But cutting back on the food amount did produce results.