I agree, this is a potential life threatening situation and WORKING with a Vet is important for diet and any other recommendations. If you are not comfortable with the recommendations of your current Vet, look for one you are comfortable with. As c4c has mentioned, you already have three Vets concur with Rx food. As written by other posters, increased moisture in the diet and frequent opportunities for bathroom breaks are very important with these conditions and overall health in general.
Here is a good site to learn more about your dog’s condition:
http://www.cvm.umn.edu/depts/minnesotaurolithcenter/recommendations/home.html
