Instructions:
1) Go to the entrance to the Goblin Mine. Die.
2) Ghost run to your corpse, go back into the cave, rez,
3) You are not invulnerable behind a teleport field and the opposite faction cannot attack you.
4) Defend the mine with pet/minion etc and/or use warlock demonic circle to move in and out as you please.
A skilled warlock with good gear can solo defend against any number of players.
(This and several other powerful exploits are in the following video)