How do you break up fighting dogs?

[Fermit The Krog and Sexy Sarah]

I was woken up half an hour ago by Sarah in tears, having not been able to break up two of our dogs fighting.

They normally all get along fine. These two have fought now on maybe four occasions since we got Beaux a year ago. The other occasions have usually been over food, getting too close. This time it was over a game of tug with an old rag. They got a bit too 'excited' then it kicked off. What upset her this time is that apparently she couldn't stop them using all of her decibels and strength. She says eventually she managed to pull Wilson far enough away to break it up.

They're a Dobe x Viz and a Lab x Brittney Terrier if of any use.

Does anyone have any ideas of what to do if it kicks off again? It's not something I've experienced in my years of dog ownership.

[Fermit The Krog and Sexy Sarah]

Thanks for all the pointers, I think we'll buy some of the sour apple spray off the bay. I also read another tip elsewhere to pick one of them up by the rear legs, wheelbarrow style, and swiftly pull them backwards.