How take make a task which fills the gap between another two task, and is automatically adjustable

Hi,

I have the following question, on which I couldn’t find and answer in google.

How to make a task with flexible duration, which will fill the gap between other 2 tasks and will automatically adjust it’s length:
Example 

Task1: Deliver building material (fix start task)
Task2: Guard delivered building material (fixed units)
Task3: Build building (fix start)

So, I want Task2 to fill the gap between task 1 and task 3. I want it to adjust it’s length depending on how late task 1 finishes. So, that it will always start when task 1 is finished, and will always finish, when task 3 starts. Is it possible with Asta?
thanks