Stop dragging annotations while moving the text

Hi ,

I have 2 annotations
a. corresponding to a data point
b. just on the graph.
and my graph is editable.

I want to know whether i can stop the dragging of annotation (a) since i want it to be a fixed point all the time…
but i want the ability for the user to move the text around…

annotation b should be work as normal… should be able to change the location & text to be moved around.

thanks in advance.