Even though he is neutered I believe this is territorial marking. Although he has been in the new place before, and territorial behavior is significantly reduced with neutering, it still occurs with some rabbits. He’s probably in the new places running free, thinking how everything smells new, and just wants the place to smell like him. Because of this, the behavior may continue until he’s completely comfy in the new place. For now, I would use vinegar to deodorize the areas he marks.

How long have you been in your new place? I agree it sounds territorial, maybe from traveling so much and being in a lot of new homes?

Any new smells in the new place? Maybe living with a new human triggered something as well?

Generally the recommendation is to restrict his space a bit until his litter box habits return, then gradually give him more space.

Perhaps he’s feeling territorial now that this new home feels like it might be “permanent”. You said you were apartment hopping. I wonder if he never really settled into any of these places.

What a cutie!

He’s actually been to my partner’s place twice before I officially moved-in and he was actually on perfect litterbox behaviour in the winter months.

Did he have the free-range back during those times?

Then spring rolls around, and we let him outside, and he’s an absolute disaster. I thought it was spring crazies, but this is just never ending.

This is interesting. It is known desexed rabbits can still have a rise in the sex hormones during spring. I think it’s from the adrenal gland.  If this is the case with him, there is still a chance this will stop on it’s own, fingers crossed. But I do wonder if he is having some early changes to his adrenal gland. We often hear of older, neutered rabbits that start to display more hormonal behaviours later in life. My own began this around age 6. It’s thought it might be similar adrenal disease like ferrets get. But it can also be pituitary gland. I wonder if it would be worth having his testosterone levels tested?

My other thought (if this is medically-based and not purely a marking behaviour) would be E.cuniculi.  Some incontinence can be a symptom of active EC infection. Is he very deliberately peeing or just seem to be unaware?

Either way, it looks like you might have to restrict him some. 🙁  The four litter boxes reminds me of a member who had to retrain her rabbits litter habits. She did this by having the pen basically filled up with litter boxes. As the rabbit improved, she was able to take them out one by one.  Even a pen and one box would be good to observe him in for the time being. To see if he is actively avoiding the box even in a smaller space.

Back to square 1 with reduced territory slowly opening it up. If you can add a litter box (if you haven’t already) in the open area that may help as well as he may be more willing to go there than to go all the way back home. I would suggest, if at all possible with arranging pens, to start with the largest area you know he can responsibly handle and move the pen out an extra few feet every few days. It’s a pain but it may help because he can smell up just that small area at a time so it smells like him and not be so overwhelming with ALL the space. You could also put a pen in the new area and have him play there just in a small pen with a litter box, so also allowing him to get his scent on things but hopefully in that confined space he’ll be good with the box. I have 3 rabbits who are still bonding and their litter habits are atrocious near their house and the litter boxes but I have 0 issues out in the larger play area so I think it’s a matter of giving him more time to acclimate and adding another box or two. It’s possible your house is bigger than mine too, of course, so you may have more work than I did to get him behaving the way you want