2 year old neutered male cat is peeing in the fireplace
Maisie and Cosmo
I think it is because a previous cat who developed a bladder cancer previously left his scent there. (Cosmo is half of a bonded sibling pair and has no problem using both litter boxes.)
So far putting foil down on the bricks works but after removal months later, he did it again. I live in an historic home. The hearths are old bricks set in sand so it's very hard to impossible to eliminate odor.
I use a pheromone diffuser, and cat attract herbs in the litter box. I have looked into motion sensor deterrents but they seem cruel. Citrus scent doesn't seem to work well either.
My thoughts: I'm sorry to hear that your cat is having issues. If he's attracted to the scent of another cat, and now to his own, my suspicion is the only way to solve this is to cover the area with an odor neutralizer.
I'm not an expert in fireplaces or brick, so what I would do is consult with someone who is, and ask them what is safe to use on the materials the fireplace is made of.
From my own experience with home ownership and cats, distilled white vinegar is often safe to use on many surfaces as a urine odor neutralizer.
Vinegar is commonly used to remove odors and as a cleanser, and has been recommended to me by tile care professionals. I don't have any brick surfaces in my house, though, so again, I would ask a professional about it before using it.
If it's safe to use, you might try a solution of vinegar and water in a spray bottle so you can soak all the vertical surfaces. Another option would be something like Fizzion, which is a CO2 based cleaner, but again, I would make sure it won't harm the fireplace.
You may need to do the treatment more than once to get it all. A black light can help determine if there are residual urine stains so you can do any touch up needed.
I hope that helps and I hope he loses his desire to leave his mark. Please let us know how it goes.