Maybe give it an ability so its always on top of the stack? Or maybe that won't work..
I was thinking of this concept myself (mainly for some interesting Type 4 cards), and the best wording I came up with was:
While ~this~ is on the stack, no other spells or abilities may be put on the stack.
Of course, I've never liked cards that sort of 'break the fourth wall', so to speak. I know not many people do this, but if someone were actually trying to think of their game as a duel of planeswalkers, what the hell is 'the stack' to a planeswalker? It's a rules thing, not a game thing; it has no in-game flavor. (Side note: It's for this exact reason I think Mirror Gallery is really really dumb. At least, the wording is.)
Okay, end rant. Technically though, the wording should work, but my only problem is that it's unclear what happens to triggered abilities that trigger when this spell is put on the stack (say, Decree of Silence or Standstill). Do they wait for this spell to resolve, then get put on the stack? Or are they just prevented from happening altogether? So I propose a minor modification:
While ~this~ is on the stack, no player may play spells or abilities.