Hi KC,
I’d recommend you go to http://www.itchnot.com This is a website from a veterinary dermatologist and has loads of good information. On the left sidebar click on CE notes. The combination of “ears and rears” is apparently one of the hallmarks of food allergy! So when you mentioned that your dog’s belly and privates are very dark that rang a bell with me. You may want to see if your vet thinks a food allergy may be the problem.
Here is some info on doing a food trial. http://www.veterinarypartner.com/Content.plx?P=A&S=0&C=0&A=2499
I did one with my dog.. his problems were GI related but we cleared the problem. Oh… when tested I found out that a lot of the “limited ingredient diets” you can purchase in stores have tested positive for proteins not on the label whereas the vet versions tested “clean” So If you are going to do a trial I’d use a vet version. Good Luck
