Somewhere I had heard that baking soda might be effective at lessening stains. The trick is to clean and dry the wet area, once discovered, then put dry soda down afterwards. It is amazing how effective it is at stopping stains from darkening. I think that it isn't a good idea to actually use it wet, it seems to remove moisture and neutralize compounds in the urine. Its pretty amazing, easy to sweep up dry, and no odor remains after use.
The best idea for soaking pet urine from the cracks in the wooden floor is to sprinkle baking soda on the boards where needed. Leave it for an hour or two and you will actually see the urine sucked up like a straw.
Nature's Miracle. Buy it in the pet store.
This is a great article for that. It will also help with stains! https://www.angieslist.com/articles/hardwood-floors-getting-rid-pet-urine-odor.htm
Thank you all for the advise! I'm hoping the hydrogen peroxide and baking soda will do the trick. The stains are nearly black on my maple colored floor. I may need wall to wall carpeting now. There is no odor, just the dark reminders of my very old German Shepherd.