WSB,
Try setting the "Finish-to-Finish" constraint on the relationship between
the two tasks. This will require that in order for the linked task to
finish, it's predecessor must finish.
Go to the Task Information view by double-clicking on the dependent task,
then select the Predecessors tab. Enter the number of the predecessor and go
to the third column (Type). You will see a drop-down menu option and select
"Finish-to-Finish" as the constraint.
Using this, the second or dependent task finish date will follow along with
the actual finish date of the predecessor task.