k. (disables a crashable unit and ends debate)
As for the relevant topic *cough*, one more thought: burrowing. You can't really click it rapidly, but you could slow down units being ordered to move by getting them to burrow. Might add an additional element of strategy. With lots of units, you'd have to work frantically (or have the sense to use hotkeys on groups of 12) to slow down your own units enough. Plus you could have it be purchaseable to boot.