Science Diet RD

He doesn't look fat enough to be put on an obesity diet. I've seen some faaaattt dogs, and yours doesn't compare to the fatties I've seen

 
  I agree; Jessie looks very similar to your dog's body condition and she needs to lose about three pounds; we had tried a new food and it didn't have k/cal per cup on the bag. The formula I used to calculate k/cal per cup was incorrect and I thought the food was about 360 k/cal a cup. After several weeks I thought she was gaining weight and had her weighed; she had gained six pounds. Kelly sent me a link to Mordanna's board and it said on there that the food was 551 k/cal per cup; she had been getting over 600 hundred extra calories a day. [] To maintain her at 62 pounds she gets about 850 calories a day; she is also walked an average of seven to nine hours a week.
   That's great news about your cat.

he looks like a typical protein-starved grain-fed dog to me: poor muscle development, depositing fat under his skin, gradually losing his waist. A well-muscled dog, even if overweight and thick-coated, should have hard, large, very visible thigh muscles, and I don't see any on him.
I would find a low-carb, nutritionally dense food that contained close to 30% protein and feed a small quantity of that. The problem with feeding a prescription diet food for a short period of time and then stopping is that any weight lost will just be re-gained after stopping. Like humans on diets who then stop the diet.
A really big problem with feeding carbohydrate-laden foods to fat-prone dogs is you feed very little in an effort to cut back the calories, and you end up also cutting back the essential nutrients like protein, and vitamins and minerals to dangerously low levels. Dogs have no nutritional requirement for carbohydrates. All carbs contribute to the diet is calories, which your dog doesn't seem to need. It would be much healthier to switch to a low-carb, nutritional dense diet.

KayCee was on SD r/d for a few months, lost her 15 pounds that I had been u nable to bet off her, has been off the SD for over a year and not put any of the weight back on...come to think about about, she has been off for 2 years.