Work situation - what would YOU do ?

My boss's boss (and there is no one higher i can take this to, he's a director) wants me to do something that i KNOW will be bad for the future of the company and i KNOW that, however much i cover my arse, when things DO go wrong, as they inevitably will, i am going to get fired for it.

But if i don't agree to do what he says, he will fire me now.

So i can either

1 ... refuse and i stick to my belief and prediction of it all going tits up and get fired now and go and get a job elsewhere (which will be quite easy and it will probably pay more, but may not be a job i enjoy as much), ......
or
2.. i can do what he says, and keep my job, and oversee the inevitable carnage (but in our industry, within my small enclosed circle, the "disaster" will effect my future job prospects) and get fired later

Should i

1.. get myself fired for refusing to do it
2.. do it and then get fired when it all goes wrong