I don't have to worry about contamination too much in my yard. There aren't any animals who do their business there except for along the sidewalk and I don't put my guinea pigs near there. They stay closer to the house.
Found this old picture of Mr Bubbles in my cloud. Reminded me of when he was young and before he got too fat and out of shape to get up there. We've long since gotten him slimmed down to a good weight and in top shape, but for some reason he doesn't get up there anymore. I believe he's the one who taught Scruffy to do that. Or maybe it was the other way around. I can't honestly remember.