The secure checks will be made in the php file.
If char votes at more than 12 hours form last vote, add point, if not, dont add anything. Also you cannot be sure they vote because the point is added when they click the link...you got no idea if they type the security vote on the voting site and press the vote button too.
Anyway there could be one more check. If the vote is 12 hours laster then the last and 5 seconds after the link is clicked the vote count increases too (import it from the voting site page), then, add...100% secure.
Because I dont know php at all I request some web coder to do it please...Would complete this share and be totally pro. ^^