Initially, we separated them when they were strangers to each other. Somehow, one of them poked her nose into another hutch (freedome of navigation LOL) and got a bit of her nose bitten off. It cost us AUS$60 vet fee. We got them sterilised (costing more AUS$). One of them is still quite aggressive. It is o.k. in our backyard as the other can just run away upon any sign of the other being aggressive.