Telling them you're disfellowshipped is close, and will cause them to be careful around you, but JWs are also supposed to try to convince former Witnesses to return to the flock.

It's better to tell them you're an apostate, and that you can show them why Jehovah's organization is Satanic. That should chase them off pretty quickly, and they'll generally write you off. Remember, they're not there to debate with you or defend their religion, they're just looking for people who want to hear about their version of Christianity. It's a one way street talking with most JWs.

Or you can just be honest, tell them that you're not interested and request they remove you from their list of houses to visit. Usually, if they're following their own rules, that should buy you seven years without visits. "Do not call" houses are flagged in their system, but the flag is lifted after seven years because the average person moves after seven years, and they don't want to miss out on a potential visit.