Hmmm. Not sure about the decomposing part. But so far it is sometimes a bit difficult to find Indigo's feces (urates are easier since they are white), but he's still young and his 'presents' are small so I'm thinking it will be easier when he's older. I can usually smell it and I know there's something I need to find - plus I know based on his routine. I just sift through the substrate with one of those kitty liter scoops.