Seems like the ONLY assurance is to have it under the state or federal park program.
Note that this was not public land -- it had been owned by the Hawaiian Pineapple Company and then Castle & Cooke, so this is not a public to private ownership transfer.
Wikipedia has the details: http://en.wikipedia.org/wiki/Lanai
I also read of the added costs of cleanup after the latest meth-lab/pot-farm bust finds terrible accumulated waste and in some cases, caustic chemicals left behind... Illegal operations have little incentive to be kind to the land.
A state or federal park program is about as far away from an assurance as you could get. The feds and states sell off land all the time for development, and given the entire US Government system is bankrupt, that trend will accelerate.
You can get a "recreation permit" for one small part of the area (Midway Atoll), so the entire area is not closed off, but for the most part it's all "protected".
There are more, but I assume you know how to use Google?
If they did, it would probably become poacher central because nobody would be there to stop them. (Come to think of it, maybe it is like that right now, who knows?)