Maybe other stinky, disgusting animals that have gotten in by jumping the fence and climbing the trees. Or if it's a girl dog it could be rolling in its own urination. Or just bad-smelling grass and mulch.

dead animal. My dog's do that. It's not cute.

Your dog may have developed an ear infection most commonly caused by allergies. Or may be stinky due to what you are feeding, which can ALSO include having an allergic skin reaction to the feed. Read over your feed ingredients, if there is corn, it is likely the offending problem here. While some dogs do just fine with a corn based feed, it's not really optimum for digestion and good health (but some do thrive on it...we are all individuals including dogs!) If the dog recently had vaccines, they to can cause allergic reactions, including skin problems that can result in a foul smell. IF the ears have brown, or black gunk in them...there's the source...however, pin pointing the exact cause, can be a bit of a pain in the butt! The Vet can do allergy tests, but they are expensive and just as likely to be INCONCLUSIVE OR WRONG as the allergy tests done on humans! My Vet suggested (when I had a dog with this problem) that rather than spend all that money, which I was in short supply of...that I become familiar with the ingredients in my feed and then try SWITCHING to ones that were different. It took a bit of time (buy only small bags if feeding kibble!) but I DID figure out what feed would NOT cause the problem. Another dog, our Coffee girl (RIP/lab) was allergic to GRASS...more than about 4 to 5 minutes at a pop more than twice a week...and she would break out in HIVES, and end up with ear infections, that stunk to high hell and annoyed her all to pieces! ...trial and error and paying major attention to what the dog was exposed to was the solution for her. Here is a site to start learning about dog foods...and remember even a high priced feed CAN cause problems for SOME DOG OUT THERE...anything ingested, applied or exposed topically, or medicated with WILL CAUSE a negative reaction in a given number of individuals, exactly the same as with humans...someone, somewhere WILL have a negative reaction to it! http://www.api4animals.org/facts?p=359&more=1 Nutro feed it not too pricey and is generally pretty good for MOST dogs... and I also like Nature's Variety http://www.naturesvariety.com/ Remember too...if you are using toxic flea and tick drops...more allergies...Try NEEMS oil instead...it works and is NOT poison...frontline, advantage and other commercial products ARE poison..for YOU and YOUR dog. Whole Foods carries Neems, or you can Google it and buy on line or ASK your local health food store to please order it...YOU can use it too for keeping Skeeters off of YOU! Also, do not over wash...and check the ingredients of any shampoo or condition you are using...You might try Nature's Gate (human shampoo) assorted types..I'd go with a moisturizing one...natural ingredients...and wash no more often than every 3 to 6 weeks IF YOU MUST while trying to figure out what the cause is...over washing stimulates the glands to produce more oil...which can smell...especially if your dog has a double coat (most retrievers do, while also drying out the skin...an oxymoron in my book, but it appears to be how it works! Regular brushing, won't cause over production of oil, but WILL help remove dead fur, skin, and distribute the normal oils in a healthy way. Best of luck! (It could also be Rabbit or Squirrel scat in your yard that the dog is rolling in!)