I've found this to work very well.

Purex Crystals laundry softener.

I keep a clean yard but with all the snow we've had and hay lying around in the areas there is a slight odor.

I bought the purex crystals and did not like the smell in my clothes. So before I threw it out I looked over the ingredients.

Ingredients: Sucrose (sugar), Bentonite (clay), PEG Distearate, Fragrance, Sanolin Blue ( colorant)

I just used it to sprinkle around the areas, not within them and lightly wet the ground. I suppose you could sprinkle it in the areas, my guess with the sucrose, they might try to eat it. It smells fresh the way I applied it though.

It has lasted a few days thus far, also use lime a couple times a year as needed.