We rescued a male bunny from one of my sisters friends (they were gonna put the poor thing on eBay) and bonded him with our two previous females. Think it was more luck than anything but within a matter of weeks he was out roaming the house with them and now (we got him in January) he is living with them permanently. Anyway in order to bond them we had separate cages and when we let our girls out we would put him in their cage so that he should get used to their sent and them his, the cage he cage was always open for them to go in and use as they wanted. We also kept the cages next to each other so the smell was always close.
In the end though I think we were very luck as within about 9 days he escaped while I was feeding him and just snuggled himself in the middle of the girls and we never looked back
Not sure it could really be that simple but good luck with your bunnies
Is he neutered, could be the smell of an unneutered male making her aggressive?
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