I'll just clarify a few things first.
What I consider as being the stack of death is when a powerful stack is created early, and the player or AI focuses troop creation on that stack. It is not that creating a powerful stack is bad, it's is just that the stack of death is a very powerful stack that represents most/all of the players power.
1. I've posted some strategies before for dealing with single big stack cheese very early in the game, that applies thoroughly here. One stack just cannot track multiple targets, and with changes to movement, this will be indeed a good tactic.
2. The other ways that deal with a stack of death are strategic level spells, more spells that inflict penalties to a single stacks attributes, like movement, healing, attack/defense, initiative etc, are excellent methods of really hurting a player that has decided to put all their eggs in the one basket. So more spells please.
3. Additionally, ensuring that any spell that can dispel magic effects has a cost that is relative to the number of effects the stack contains, would be a wise move.
That's it really, and stacks of death shouldn't be as big of a problem as they are. Lots of stacks of death? Well that just means that your loosing big time and is not a cheese.