Now that 2.4 is out almost EVERYBODY is at the Shattered Sun offensive at the Isle of Quel'Danas.
Well, there are guards there to prevent hordes from killing allys and vice versa.
However I also noticed that you can duel your own faction there, so what you do is challenge someone in a duel and wait for them to attack you,
a few seconds after that they should get ZERGED by guards, die, and loose 10% of their durability giving them a repair bill
Use it wisely!