A good start would be to make it a crime for anyone on a sex offender registry to be in any place like this.
Sure, its like a restraining order against someone who is trying to kill you however its at least something.
There are lots of things that can be done. Heck I am all in favor of a notation of a drivers licence or state ID for sex offenders, show your ID at the gate if its got a red border around it then its a no go for entry.
While not perfect, international guests could show their overseas ID and you could argue that since they have come into the country they have been somewhat screened already by homeland security.
Yeah I know its a PITA, It will slow things down and people might not be thrilled with the idea, personally I don't care if it helps keep these perverts away from my wife and children while they are playing then so be it.
As far as I am concerned when your convicted of certain crimes you give up the right to certain things in society.