What do you recommend for a large dog urine spot that wasn't noticed?

I'm assuming it was on carpet? Try Natures Miracle. It breaks down the urine crystals...you saturate the area and then leave it...allowing the product to work. The urine smell will get worse at first as the product works. Try it on a hidden area first. I have used this product with great results

What is the urine spot on?

yeah flood the heck out of it with nice hot water, then use a folded towel and stand on the spot, move the towel until most of the water is absorbed, flood it again and repeat with towel....add some carpet cleaner for pet spots and then do it again. The trick is to get as much up as possible, then neutralize the urine with some kind of Deodorizer so your dog doesn't use that spot again. I like OdoBan I use it a lot! You can get it on line from Walmart....I'm a Newfoundland Mom so I know all about big dog pee spots! Good Luck.

White vinegar works well on urine spots on carpets.Soak the spot with white vinegar and lay a towel on it for a few minutes.