Thanks for all the details! I do think a couple more weeks of pre-bonding should help allow hormones to settle more.
So, bonders vary a bit in how much fur pulling they allow. I think if you are new to bonding, it’s best to try to prevent it, because things can escalate quickly to a fight when you are in the really early stages.
If one rabbit is very excited about food, it might be best to remove the food for now, just so his excitement over the food doesn’t get misinterpreted by the other bun. Food can be a good tool when sessions get longer, but in the beginning I like to keep the bonding area pretty bare-bones.
When your harlequin approached your lop, was it a rapid lunge, or a more tentative approach? If the later, then I recommend petting both buns a lot when they approach each other. That makes them think they are being groomed and can help them build a positive association. It is really good that you petted the buns for a while to end the session. It might be good to try starting the session like that as well.
If the attack was more of a rapid lunge and attack right away, then I definitely think more pre-bonding would be good, and that you will want to try some stress sessions (such as a short car ride together, or you can put them in a bin on top of the washing machine). Car rides have worked really well for my tougher bonds to get them past the fighting stage.
I wouldn’t recommend a harness or anything like that during the session, the risk of injury would be very high. Instead, have a dust pan or something similar handy to put in between the buns to block lunging (don’t use your hands like I do LOL, I once ended up with a bite that left my thumb numb for about 8 months!). I’ve also heard of people using mesh colanders to put between buns as they sniff each other if they suspect aggression, but I haven’t tried that myself!
I also think it helps to set super short time goals. Since you know this first session went bad after 30 seconds, have your next session be 30 seconds or less. Then slowly increase the amount of time they are together once they can spend that amount of time without fighting.
I’m sure you will make progress before your trip, but I can’t say whether they will be bonded by then. In my experience, the pressure of having a firm deadline tends to slow down the process, because I’ve always ended up pushing the buns a little too far and then back tracking. For context my first pair was like yours in the beginning, immediate fighting. I didn’t know what I was doing at the time, but it took me about 3 months to bond them. They were MADLY in love once they were bonded though, so it was totally worth it!
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.