Advice to my Friend on How to Stop Cats from Spraying

I have a friend who loves cats. He always wanted to have cats at home. I suggested him a place from which he can adopt healthy cats. As a matter of fact, I went with him on the day of adoption. I am no cat expert. But, I still gave him my opinion on choosing the cats to take home. He finally zeroed on a few good looking cute cats and he was happy to take them home. But, after a few months, I got a call from him saying that he is not happy with the cats. He actually still loves the cats. But, he is not happy with a particular behavior of the cats. He doesn’t like the cats spraying. He kept calling me to ask how to stop cats from spraying.

Even though I am not an expert in cats, I very well know that it is not possible to stop them from spraying completely as it is their natural behavior. So, I asked him to first accept that the fact stopping cats from spraying completely is next to impossible. Maybe, neutering the cats maybe the only option. But, he doesn’t want to neuter the cats and I also don’t recommend it. So, I asked him to search online to search for ideas on how to stop cats from spraying.