Thanks Mandoble.
I just tried spawning a new trigger every time and also deleting the old one through a script. This seems to work well to.
trigger = createTrigger ["EmptyDetector", position player]
trigger setTriggerActivation ["OPFOR", "WEST D", true]
trigger setTriggerArea [10000, 10000, 0, false]
trigger setTriggerStatements ["this", "{player reveal _x} foreach thislist; deletevehicle trigger; triggerused = true; trigger = ObjNull", ""]
exit
In the editor I have placed a repetedly trigger activated by "triggerused" which starts this script again.
Cheers.
Laggy