I think someone onboard mentioned vinegar for discouraging barbering, but I’m not sure.
0_o
Poor Dallas. I know how he must feel, when we got Pip she had been barbered by a hothot that was being housed with her at the pet store. She had no fur on her forehead, right between her ears. >.<
Then we found out later my husband’s cousin had bought the hothot for her daughter. So it’s like they’re still in the family, so to speak. ^_^

This was MooBunnay’s response to another member on this topic, obviously your two buns are both males, but the advice applies just the same.  I don’t have personal experience with this betw/ my buns but I hope this helps:

1) Sometimes barbaring is caused by stress.  This can be reduced by giving your bunnies a very regular schedule, for example: feeding, cleaning, and giving them play time at around the same time each day.

2) Sometimes barbaring is caused by boredom.  If your bunny has a particular toy he really likes to chew on, for example: cardboard or willow wood, provide a LOT of this for him to chew on and to play with. I gave my boy a couple big willow boxes (found them at IKEA!) and he has been having the time of his life chewing holes in them, and it keeps him distracted for a long time.

3) Sometimes barbaring can be caused by an irritation or bald spot on the skin. If your female had some type of irritation in her eye, it could have caused the male to start overgrooming, and now that there is a bald spot, he will become even more fixated on it.

4) Binkybunny found out that sometimes it is not enough fiber in the diet that can cause this. When I changed from one kind of hay to another that my boy bunny liked more, the barbaring stopped.

What to do now that there is a bald spot:

In order to prevent the male from continuing to fixate on this bald spot, you want to separate them for 2 or 3 days, just long enough for her to start growing some fur over the area. Then he won’t notice the bald spot so much and try to clean it. I did this by just using some NIC cubes to put down the middle of the cage, and put a make-shift litterbox on the side that didn’t have one. You don’t have to be very complex about it because its only for a short period of time.

As you can tell from Beka’s post – I’ve had a lot of barbaring problems Just to add a little something, I was told by most of my rescue friends that if the bunny being barbared is really in pain, he/she will usually let the other one know by lunging at them or giving them a bat on the head, so I think that if Dallas was in any pain he would make Duncan stop. I tried all kinds of things with mine, but in the end I really had to separate them long enough for the bald spot to grow some fur back because Kramer became totally obsessed with the bald spot! But don’t separate them as in actually putting them in separate cages far apart, just try putting some kind of divider between the two of them, like an NIC cube wall so they can still lay next to each other and do a little grooming through the cage.  As a pseudo litter box I used the bottom of one of their carriers for one side of the “cage” – and you can still let them have out time together, just as soon as you see Duncan trying to groom that spot, gently redirect his attention to something else.