It could be anal glands, urinary tract infection, or ear infections. These three can be very malodorous. You could wash your dog over and over again but unless you address the issue the odor will keep returning.
Bring a fresh urine sample to your vet for urinalysis. If it is not the urine, than bring in your dog to have his anal glands expressed and his ears checked.
I bet that this is either a bladder infection, or the dog has not been fixed(neutered or spayed). Once the dog is fixed, the urine is less stinky!
He needs to be seen by a vet, I'd think that would be a good first course of action.