I did some research on how to clean an outdoor rug, but all I found was using bleach. I am not a fan of bleach. The smell, the way it ruins everything I use it on (I am bleach incompetent) was not to my liking. I did a little search in my cleaning supplies and this is what I came up with.
I sprayed it on the spots and scrubbed a little. Repeat then rinse with a hose. By the time the sun was done drying it, all the spots disappeared. What's great about this product is that it is supposed to prevent it from reappearing. Only time will tell.
Now maybe I will paint a pattern on it...hmmm.