[Rules] AT Ditches, Engineers and Fog of War

[SleepyGoblin]

I am playing a scenario using the fog of war optional rule. 

In the scenario the engineers have to clear a number of AT ditches.  In order to do so they require three turns to complete the task.  When using the fog of war rules, do they need to be activated to increment the counter for each of the three turns?   

I apologize if this question has been answered in the past.