I know with Chewy, his poo had an onion smell to it. If you can neuter him, you won't be sorry. Chewy never pees outside the litter box now. He still occasionally marks with his droppings here and there, but doesn't leave piles of them, like he used to. Plus it made him much sweeter and less reclusive. I haven't had to clean his scent glands since he was neutered either, he is cleaning those on his own.