We have a few high power members in a different kingdom that are employing what we are calling "Ghost Seige" tactics. What they do is make a new account in OUR kingdom so they can sit that player on the city that they are attacking. When they attack, if any of our players move to defend or attack them, they log off of their attacking account, and use the second account to make sure they only log back on when no one is around and attack again. We cannot defend against these tactics, therefore we feel it is a cheat.
A simple solution would be to relocate a player back to their capital if they log off while in enemy territory. This would also cause very little effect to normal gameplay.