Hi, I am a certified vet tech. I have four dogs, all skinny, except for one. She has had two cruxiate ligament surgeries, a year apart. That meant she could not exercise as she normally would, for over two years, either because of injury or because she was healing from the surgeries. I was worried about her weight gain. So my vet and I together decided she was a good candidate for Slentrol.
Well, I would do it again in a heartbeat! It curbed her appetite, and it also works to discourage the intestine from absorbing the fats that it normally would during digestion. Her weight just melted off.
I don't think it is for every dog. But when strict diet and increased exercise are NOT an option, it is a great aid.
A word of caution - don't do a BARF diet or other fad diet with a dog who has a history of any kidney problems. You could end up with serious health issues or even permanent damage. Other people here recommend various high protein diets - again, a diet abnormally high in protein (for a dog, cat's are different!) is NOT a good thing for kidneys. These diets are fads, and people are making money off them. They aren't based on sound science, for the most part (I know, I've done extensive research on them from a medical veiwpoint).
Do go ahead with the cruxiate surgery too - I'm sure your vet told you there is a more than 50% chance your dog will blow the other cruxiate too. And the surgery is expensive. But if your dog is young, and would normally be active, as mine was, it is totally worth it. She was 3 for the first, 4 for the second, and she is nine now and active and not in pain as she was.