@ legowarrior
Your idea of how NAP agreements are cancelled has been suggested before.
http://forum.shrapnelgames.com/showthread.php?t=40012
Unfortunately (in regards to the merit of the idea) it was suggested by the all time master Court Jester and all round laughing stock of the community, and was wildly regarded as one of the stupidest ideas ever seen on these forums (which was a real achievement considering the regularity he came up with such rubbish).
It was mainly consider bad because it's easily possible in just 3 turns (typical length of NAPs) to have conquered every enemy province, and have every fort under siege. So while this idea might work in other games, in Dominions it is just simply out of the question. As if anyone is dumb enough to just sit there and let someone conquer all of their lands, and kill all their troops just to honour an agreement, then they really need their head examined.
And you can try to say that's the price of cancelling a NAP, but when applied to practice it would mean it is virtually impossible to cancel a NAP with an major nation without instantly condemning yourself to defeat. And that scenario is seriously terrible for all sorts of obvious reasons. Not least becuase enough turlting (and terrible strategic play) goes on anyway, without applying such hand-tieing binds. (as such this idea just won't work in Dominions)