Smelly piles are caused by too much water, no air, or the addition of meat or other animal products.
Fix these problems by:
Mixing fresh grass clippings with stalks or brown leaves to help air get in.
Keeping the pile as moist as a wrung-out sponge, but not soggy.
Turning wet or soggy piles to let air in.
Keeping food waste out of yard waste piles, and animal products out of worm bins or food digesters.