Anyone have experience with this injury?

I don't think this would constitute and emergency since he is not bleeding or seemingly having any problems. I would just keep it wrapped, clean and dry. If your yard is muddy or you have puddles, you can put a baggie on this foot with a rubber band for a short time while he goes outside to eliminate so no moisture or dirt gets into the bandaged area. Next time you go shopping, go out and buy some Betadine Solution. This is great for cleaning wounds such as this as you should not use Peroxide to clean a wound such as this. Have a safe 4th yourself, and Thank You for serving our country. (I read your profile)