Civilization V's elimination of unit stacks was a big deal when 1st announced, and now has people asking developers of 4x & TBS games whether they are going to have "stacks of doom" in their games or not.
I just got this idea while falling asleep last night. A potential solution to "stacks of doom": pincer attacks.
If a stack is attacked in the same turn (or simultaneously, depending on the game design) from more than one direction, it receives a penalty relative to the #/positioning of attackers, as well as the size of the stack.
This represents the difficulty of arraying a large army, with its greater reliance on baggage trains and camp followers, against harassing tactics. The alternative is not stacking (putting army in a column).
Thoughts? This just came to me.