Marty, there are several prescription diets available, you don't have to stick with just one. Here is a link to
Veterinary Diets, this page is for cats, but the same applies, your options are available there.
No, vets do not get a kickback. As a matter of fact, getting cost isn't that much at all.
As for incontinence, it may be a life-time condition, not necessarily related to history of stones or the present surgery either. While it may improve after yesterday's surgery, be prepared that it may not. In any event, your vet can tell you about the various medications available to help if you're not approaching that already.