You start by having an amnesty on unreported finds. All finds must be reported and certified. All items offered up for amnesty get assessed for national heritage importance and reasonable compulsory purchases are made if necessary. After the amnesty dealine nothing can be sold without authenticity and certification. Very large fines (and prison sentences for repeat offenders) are put in place. All new finds must then be reported or they become unsaleable

Once you have a clear system in place the rest becomes quite easy.

You do not want to go down the route of blanket bans or permits. In Ireland a permit system exists, but only Universities and privately owned archaeo companies can get them. Undoubtedly nighthawking goes on in Ireland, but I believe they say they don't have a problem with MD-ists because MDs are illegal. D'OH!

The Universities can't really afford to do loads of work and the private companies get the rights to whatever they find (albeit sometimes just the intellectual rights/image & info copyright for a limited period). It's a system that is, basically, a crock of shite!

What we do need are honest amateurs out there doing this, but the honesty does sadly need thrusting upon some of them.