Hi there There are many enzymatic products on the market including Nature’s Miracle. The best is called Anti-icky poo by Mister Max, it’s good for all sorts of things (like getting blood out) but it’s expensive and only available through a distributor. he will still stink for a bit after he’s neutered.
also for some cats it becomes a learned behavior and neutering doesn’t stop it, one of the reasons we reccomend neutering before they start! good luck!