Neutered boy spraying

Flaired advice because I need some

I got my orange boy neutered Feb 2024, he was about 1.5. Recently, he sprayed (on my stuff), then again today. It stinks like territory spray, and I do have reason to believe he’s territorial.

A bit after he was neutered, I met (and took in) a stray/feral. They don’t like each-other. He’s older (estimating about 5?) and not neutered, and definitely with a feral personality. He’s gotten on really good terms with his humans, but GinGin absolutely hates him. He’s staying in the bathroom, but we do let him have closely monitored out time or put the others in the bathroom / bedroom. I think GinGin is marking territory. My Lucy did that when I fostered a pregnant mom/ her kittens, peed everywhere orca may have slept, stopped when orca went to adoption. Domino will be neutered soon.

Whats a good way to stop this? Or at least make it so hes not peeing on my art supplies? He’s targeting my yarn :(