France '14 Digging Questions

[Compass Rose]

If you have a unit in the process of digging for several turns, which has already completed a improved position and is attempting to dig a trench, then order them to stop digging so they can fire on the enemy for a turn or two, and then have them continue digging a few turns later, will the "digging level" continue where it left off (some where in between a IP and trench) or will the "digging level" reset to a IP, and they will have to start all over again for attempting to dig up to the next level which would be a trench?

Also, I had several fixed units who I set to dig however, when I get a turn back from my opponent none of the fixed units are digging, none of them have created a IP, none of them have fired on the enemy, and none of them have not been fired on by the enemy. Any idea why they are not continuing to dig on their own?

Thanks