I'll follow along to see what others recommend. I just wanted to put my two cents worth in, but it's important to distinguish between normal doggy breath and the foul knock you over odor that is caused by some type of infection.
I haven't encountered it in my dogs so far, thankfully, but I've run across it in a lot of people. I defer to those with more medical knowledge but I suspect that in many cases it's caused by bacterial infection of sinuses, tonsils or possibly dental caries.
In such cases the only effective remedy is treatment of the cause.
I brush my girls teeth a couple times a week with a doggie tooth brush and doggie toothpaste. I also give her a marrow bone every so often which helps get tarter off. If it is really bad, maybe talk to your vet about getting your dog's teeth cleaned at the vets.