How Do I DISABLE AN Event?

Given this scenerio:
Person walks forward while up-arrow is pressed.

Now:
The person disappears and I no longer wish the up-arrow to trigger an event for the 'person'

How do I stop the event-listener from monitoring the up-arrow key-press?

I think I just solved it:
The up-arrow event calls a method such as MoveObj(Object obj). Then the code within the method does something like:

while Obj.isShowing == true
move the object.

Now, might I include within that method an if/else statement so that I can transfer the event handler to move a second or third object??? In otherwords, based upon some condition, I can force the event handler to control multiple objects?
if obj1 isShowing
...do this
else if obj2 isShowing
...do this
etc., etc.

A 2nd question, does Alice recognize the instanceOf command? And if so how do I invoke it?

Any speculation on why any of the above would not work?

Thanks.