It does sound like the peeing is marking, which means it will stop eventually. You could put him back in his own pen for a day or two, and try again, to see if it’s just the stress and marking. He may not like Fern’s smell in his pen either, but if it’s medical, it would probably continue in his own pen. See if he doesn’t do it so much in his comfort zone. This will take time, so be prepared to clean a lot for a few weeks, but not forever. (I keep a covered trash can, like a diaper pail, next to Samantha’s cage for easy disposal of litter and paper towels. It keeps the mess and smell down very well.)

Dexter did that too. He still does it occasionally but 9 times out of 10 he makes it in the box. Once he was in with the others he grudually got better and better and then it just seemed to almost stop.

Well, I think I would not let Neo actually into their pen since it’s their territory. It is possible it was either marking or fright, but you cannot really know for certain I think.

Jack is very territorial with our cat. He will mark up the place if Kitty shows too much interest in the bunnyroom, HOWEVER, that has lessened over time as Jack has slowly gotten used to him, but he just got more so with his “claiming” Vivian WHEN our cat comes around.

I say give it some time, and see how it goes. Once he realizes that Neo is not showing too much interest in him or is not a threat that may help.

It can take several months. I know with Vivian and Jack, the marking and peeing was so out of hand. But now the territorial poos are limited to “near” the box, and for the pees, (which finally stopped last week), I put placemats in the favorite “pee” marking areas.

Also, I took their favorite treats and cut them up into tiny itsy bitsy pieces and put them in the litterbox throughout the day to encourage litterbox use, because it seems that no matter why they go in there, they smell the box and have the urge to pee, and it seemed to help encourage litterbox use even during marking.