Banning foreign donations

So, afte rewriting electoral law to reduce transparency over party funding, National's Nick Smith suddenly wants to ban foreign donations to prevent "foreign interference". It's pretty much a no-brainer, but what would it actually entail? At the moment, the law prohibits foreign donations above $1,500, but there are two obvious ways around it: making multiple "anonymous" donations below the $1,500 threshold, and using a New Zealand-based corporate shell to launder the donation. The first is easily fixed: reduce the threshold to a nominal level, and align it with the party and candidate disclosure thresholds, so that every non-trivial donation is publicly declared and subject to scrutiny. The latter would require effectively banning some or all corporate donations. There's a strong argument that the right to donate should be limited to natural persons - eligible voters - but people should also be able to do collectively what they are entitled to do individually, which suggests there should be some exemption for democratic, membership-based organisations such as incorporated societies and unions. while that is also potentially open to abuse, it seems a lot less so than at present, when anyone can set up a New Zealand company and use it to launder donations to whoever they wish.