The two visiting males are encouraging Casper to spray as he's marking his territory and letting them know it, and perhaps he feels somewhat threatened or at least uneasy with them coming up on the deck. The fact that you're leaving out food is why the visitors are coming to check out if there is any. Even if you're going to be home late, I would not leave any food out at all, and Casper won't starve in the meantime. Only feed him what he will eat up at one time which he will do if he's hungry. He will soon adapt to a new routine. If after some visits, the visitor cats never find food out, they will likely not bother to come any more, and Casper won't feel the need to mark his territory.
So is he marking now because the two other cats are males? The other possibility that occurred to me is that he didn't spray before either because he's willing to share his turf with my cats, or because he sort of knows that it's actually their turf, not his.
Yeah, I used to always take his food in, because of other critters (raccoons and opossum). They did stop coming around, but I've caught the two cats on my deck a few times. Casper's usually good about showing up when I come out, so I guess I'll have to go back to always taking his food back in when he's done.
Since he's been spraying even though the other cats haven't been out, I'm wondering if he'll eventually stop when they stop coming up on the deck or whether he's just going to continue.
Can you get these other two cat neutered? They may stop once they feel they dont have to mate and mark their territory.
I don't know for sure that they're males - just my guess since Casper never marked when it was just my girls out there. But I do know that they're both owned, and I'm pretty sure they're neutered. The people in my neighborhood are pretty responsible pet owners, and they haven't ever seen them come up when my girls are out there. I can't get close enough to tell though; they know I don't like them hanging around, so they run off when they see me.
I'll see what happens when there's never any food out anymore.