We've taken one of the gerbils out now, and put her in her new cage. We haven't seen either of them do it now their on their own, and they both seem a lot happier. The one we left in the main cage has started digging again, which she stopped doing when they were fighting; and the one we moved has been running around her new cage, and she's made herself a little nest in it, and she just seems a lot happier.
I do think it was the right decision separating them, because now neither of them are getting hurt.
Thanks for all your help everyone :]
 oh, and before we separated them, one of them wasn't eating. The other one kept chasing it back down to the bottom of the cage. So we started putting food down to bottom for her, and the other one kept taking it back up. We bought two bowls, because that's what the pet shop suggested, as maybe one of them got territorial over the bowl, but it didn't make a difference. Now we've separated them, they are both eating and drinking fine.
Last edited by CookieDemons; 01-14-2010 at 06:11 AM.
Reason: Forgot to add a bit :P