urine marking and yowling

Dear Dr. Brown,
I have multiple cats. One of them, Indie, has a bad habit of spray and constantly yowling. In the beginning, we thought it was UTI that cause him spraying, we took him to the vet, after 2 shots, flush and medication, he’s still doing the same thing. My next guess was, his neuter surgery wasn’t completed. I took him to the vet who did his surgery and a second opinion. Both vets said the surgery was perfect. I have used almost every brand of stain / odor spray; vinegar, as some blogs suggested; aluminum foil covered the kitchen counters, walls….., None of them work.

I googled the possible reasons for his behaviours, it indicated stress might be one of the reasons because of multi cats in the same house. So, I bought him Comfort Zone Feliway’s collar to calm him and a bottle of spray, of the same brand, to prevent urine marking. He is still spraying everywhere, yowling all the time.

He loves to go out, I let him out, thinking it might solve the problem for both of us. Then, he got into a fight and came back with a deep wound. I stop letting him out, his spraying and yowling behaviours are getting worse.

I am running out of ideas. Dr. Brown, you have over 300 cats under the same roof. Do you encounter any cats having the similar behaviours? How do you handle it?

Please help. Thank you!!!