Possibly the best advice I was ever given by a vet (not a species I always hold in high regard) was very many years ago when I had a labrador bitch with an alarming tendency to gain weight. That advice was to completely ignore feeding guidelines. He said he had known dogs that needed as much as double the recommended amounts and others that needed less than half, and that the only time they should be referred to was when first feeding a particular food to a particular dog - and even then he recommended starting at 80% of the lowest suggested amount and then adjusting according to whether the dog lost or gained weight. He didn't think much of 'light' or 'diet' foods, he said all that was necessary was to select a food that wasn't unusually high in fat, and to feed much less.
In his opinion, and in mine ever since, once any health conditions that could lead to weight gain have been ruled out, the only reason for a dog being overweight it that it is being fed more than it needs &/or exercised less than it needs.
I can honestly say that I've never had an overweight dog since. I have had a standard poodle who got 150% the highest recommended amount and was still lean, while the lab bitch ended up regaining her figure on 55% of the lowest, finally settling on 60% for maintenance. I did give her a vit+min supplement because I was worried the small amount might mean she wasn't getting her fair share of micronutrients, but the vet thought even that was unnecessary.
Of course, if you suddenly and drastically reduce the amount you are feeding the dog will feel hungry and behaviour problems can result, but in my experience if you do it slowly, say by 5% per week, they soon adjust.
I know it sounds obvious, and perhaps a bit tough, but it works for me.
(Edited to add: No, that's not true, it doesn't work for me, sadly I lack the self-discipline to feed myself less. Fortunately for them, my dogs can only eat what I give them.)