Stacks of doom aren't scary until the highest difficulty levels and you shouldn't instaquit just because a stack of doom has entered your territory.
maybe i'm wrong in terminology, but i think if you have ways of dealing with it then it shouldn't be considered a true stack of doom.

Your suggestions are good, but my main point was that it's possible to get so far behind in development and/or diplomacy that you can be faced with a stack so large that there is absolutely nothing you can do to win. At this point it becomes a "stack of doom" rather than just an ordinary stack.