Option: lock autotarget
The keybind? It is apparently supposed to be held down.
There is also a odd option that makes you drop your autotarget (but not your clicked target, but there is no way to tell the difference visually) if you turn so that it ends up outside your front cone of attack.
I am holding down the key. It doesn’t work for skills like Leap of Faith…. nevermind
http://wiki.guildwars2.com/wiki/Lock_Auto_Target
Can be used as a detarget button, amongst other things.
It would be cool if it also kept no target when you press leaping skills which can be used for quick running away from enemies. The only solution for this is to turn of autotargeting.