Good rule of thumb is stick to what works — I think expanding in the old bonding space where you saw progress is a good idea, rather than rushing into a space and potentially hurting the relationship currently built-up.

This “new space” that you tried and it didn’t work out — is it semi-neutral (i.e., both rabbits have been exposed to it; not new)? If so, I’d use the time they are in the old bonding space to try and neutralize this “new space” as much as possible, especially if it is eventually where you want them to be long-term.

Alternatively or after successfully getting smoothly through expansion in the old bonding place, starting with a smaller space in the “new space” could be wise. Starting “big” in a new space is definitely welcoming to starting some territorialness in the rabbits (especially if it’s a semi-neutral zone).

Agree with Wick! I would work on doing long sessions in the neutral space first. Once you get to sessions that are many hours long (including a possible overnight) without issues, then they will be more ready for semi-neutral.

Where are you doing the bonding sessions? And how long have you been marathoning?

If you are just removing the barrier between their living spaces, it is expected that they would act territorial because at night they are claiming the space, making it less neutral territory. Sorry if I’m misunderstanding the situation. I use puppy pee pads on the floor instead of litter boxes, as litter boxes do tend to cause issues when added too early.

Do you mostly see the issues in the morning when they go back together? Have you tried doing 48 hours straight with them yet?

Whenever I’ve gotten stuck in a rut like this, I’ve found it can help a ton to move to an entirely new location and marathon bond there. Even when a space is neutral, sometimes the area becomes less neutral over time, and even being in the smelling range of the home-turf can cause more territorial issues.

In my experience, I either saw huge improvement in 24 hours, or I didn’t, and decided things weren’t going to work out. Do you have a friend or relative’s house that you could do a weekend marathon in? I’m wondering if you could do one more final push before making the call to just have them live as neighbors.

That’s tough, it’s hard to say whether the boxes were the problem (if only we could read their little bunny minds). At this point, what are the positive behaviors your seeing and what are the negatives? Is the main pattern of aggression based on the time of day or do you see another trigger?

But it’s OK to take a break and go back to normal dating if you need to (I had to do this with some past pairs as well, that I did eventually bond down the road). I think doing a date or two in a new space could be helpful, even if you can’t marathon there. Sometimes a change in scenery really seems to help.

What happens if you don’t intervene with the nipping? Does it resolve on its own or escalate to a scuffle?

Same with the mounting, does it just lead to some chasing, or does it turn into a fight? Mounting is be OK (and happens in bonded pairs too), and if the chasing is due to a mounting attempt it may help to just observe and let it play out for a bit as long as it doesn’t start escalating (rather than immediately intervening).