I have four ferrets but they don't all get along. Each pair of ferrets doesn't like the other. At the moment they have separate play times outside of the cage. They're also caged separately in case that wasn't clear.
I've tried letting them fight it out to work out their dominance issues repeatedly over a period of about a week at a time. I also tried doing this for one month with no visible change in behaviors.
What I did was let everyone out of the cage and let them have it. I tried to keep them busy by playing with them and their toys and distracting them from the other ferrets. If there was a scuffle, I watched for any violent biting, grabbing, and rough shaking (ferret grabs the back of the neck and shakes violently from side to side). If I saw any of this, I would pull the fighting pair apart and put the aggressor in a "sin bin", a cat carrier, for three minutes to let them know this behavior was bad. Despite trying to be as consistent as possible, I've had no luck.
There's never been any injuries that involved blood or breaking skin, just a minor irritation from the biting. No one's ever peed or pooped from being too nervous or scared either.
One pair is clearly more dominant as now the other pair tends to just run and hide and wait for me to put them back in the cage. They also lose (at least I think they're losing) most of the scuffles that happen.
Is there anything else I can try to get them all to play nice together?