Think this through.  I know someone who is banned from a hotel/casino in Las Vegas.  How are they going to keep him out?  

They'll do what they can but it probably wouldn't be that hard for him to sneak back in but if they caught him it would make the criminal penalties for trespass a bit more severe.  He knows he's banned, but only a handful of employees at that place ever saw him.

It's not impossible to enforce, but if the kid behaves himself next time he might just get away with it - and you know what?   If he doesn't cause a problem or draw attention to himself that's probably for the best.

And I seriously doubt that guy I'm talking about is ever going to try to get back into that hotel/casino - I probably won't either although I'm not banned from there.