Have you tried stressing them prior to bonding? You can put them together in a box or laundry basket on top of the washer, or try running a vacuum just outside of the neutral space.

I wouldn’t throw in the towel just yet. Bonding takes time.

I agree with Beka. You should do some stress bonding. Aggression is usually as a result of mistrust and stress bonding is the best way for them to gain trust. If one thing is not working, try another.

I came to have four rabbits in my care recently.  Two females, and two males. 

Three of the bunnies had no chance to meet before I started the bonding process, a situation that happened in this case, but one that I would not recommend, if it is at all possible to avoid.

The two males, Sebastian, a one and a half year old, Checkered Giant, 12 lbs., and Dunn about a one year old lop mix, about 7 lbs. fought full out EVERY TIME I TRIED TO PUT THEM TOGETHER.  Serious fighting.

I tried coerced closeness, where I lay them next to each other between my legs and held them down so they could not bite (you might want to try this in a small enclosed area, with thick jeans and gardening gloves), their heads toward my feet.  I stroked them till they clamed down.  After two 20 minutes sessions, they could lie next to each other calmly, but I was vigilant for either one trying to bite!

This worked, but as soon as they were free, they would try to attack again.  I was afraid to put them in a basket, long enough to drive them around for a car ride stress bonding, so I tried something I read on another House Rabbit site.  I put them IN THE DRYER!

You put them in a cool dryer, and of course you do not turn the dryer on.  But the metal, curved surface keeps them from being able to get their footing.  And the second they start fighting, you turn the dryer drum, by pushing one of the extended ridges in the dryer, causing the rabbits to fall all over themselves.  Stop, when they stop fighting, but be at the ready to turn the dryer again as soon as the fighting starts!!!

I tried this both with keeping the dryer door open just a crack, so I could keep an eye on them and also stick my arm in when I needed to turn the dryer.  I also use a piece of cardboard that I pressed against the opening, leaving just the top two inches uncovered.  Sebastian, “Bas” my big, strong, Checkered Giant, made quite and effort to escape several times and I had to push him back in.

I also set a timer for 22 minutes, and pulled up a chair, before I got started.  Depending upon how big your bunnies are, you might want to get help.  It was VERY HARD TO TURN THE DRUM with nearly twenty pounds of rabbit in the dryer!  For the first 10 – 15 minutes of both sessions, there were only brief breaks before one of them, usually Dunn, would start nipping and attacking, so I was turning the drum a lot. 

I did two 20 minute sessions, on two consecutive days and they never fought after that.  They nip and bicker and pull hair and have skirmishes, and I WOULD NOT TRUST THEM ALONE.  Dunn has even bitten Bas hard enough to cause Bas to scream twice (chilling).  But it stopped the fighting enough to move on with further bonding.

After the second 20 minute dryer session, I put them in a plastic laundry basket with a grate covering it and a brick and put them in the passenger seat of my car, and drove them around for half an hour.  (I pre-staged this, and had everything ready to go, so I could just pick them up out of the dryer and put them right into the basket and walk right out the door to my car.  A good deal of bunny bonding is preparation.)

I am bonding four, so, every half hour, I added a bunny.  It worked very well.

I wound up having to take a week long break in working with my two males, and after the week, they fought again, so right back into the dryer they went, again followed by an hour and a half driving session (this time all on their own).  That was three days ago and they have been together, except for a short break, under constant supervision, ever since.  As I said, there is still biting, lunging, grunting, thumping, but there has also been grooming of each other, sharing pellets and salad and sleeping next to each other, all in a VERY SMALL BONDING SPACE, and with support, as I intervene when the bickering gets intense, with a spray bottle, loud noise, yelling and a hair dryer.

With the terrific help of Binky Bunny bonding expert TanLover14, we have made great progress.

So, in answer to your question about instant aggression, yes, you can move past that, and no, it does not mean your situation is hopeless.

One more thing, I had another pair of bunnies, two females, that seriously fought at first, they were easier to shift than my current two, but the became devoted friends and constantly cuddled.

And, I am following TanLover14’s advice and I am doing a power bonding session, that started on Friday, and once I started I am trying not to separate them at all, not even overnight.  For my two males, every separation put them back at square one, with nervousness and aggression.  All four of my bunnies are in very close quarters (in a 2 and a 1/2 foot by 1 1/2 foot dog crate) with constant supervision.  The first two nights were brutal, very little sleep constant skirmishes, but today has been great.