ORIGINAL: NotOneStepBack
Is there any special way you dig in, such as building fortifications, or do you mean just hold the line?
The longer a unit stays in a hex the better the fortifications in that hex become (click the fort button to se the level on the map). How fast it build depend on the contruction value of the unit (I'll guess). This value can, as I understand, be increased by assigning pioniers.
Units staying in level 3 and 4 forts or big cities/urban areas have the best chance to stay put during the blizzard turns.