I read that the only way to actually stop a country (that is determined to make a nuclear weapon) is to destroy its ability to do so and then prevent its reacquiring the ability.

1. Destruction of its specific industries tied to nuclear production support (most of these also have duel use).
2. Destruction/removal of all nuclear technology
3. Detention or death of all trained personnel
4. Banning of any educational aspects of nuclear technology to include dual use technology
5. Detention or death of all politicians or leaders supporting said plan
6. Rigourous in country verifiication
7. Permanant embargo on outside sourcing for materials

Essentially very difficult and unless follow up verification is done, ultimately it fails. The most viable preventive measure, #3, would not be possible in the present western world mindset.