title: Best way to prevent a user clicking 'like' multiple times
body: <p>I'm implementing a like feature for a site I'm working on.  A user doesn't have to be logged in and they can either like or dislike a particular page.  At the end of it all I'd like to be able to populate a list of articles or stories with the most likes.</p>
  
  <p>I have a  very simple method that currently uses an onclick javascript function to update a database via ajax and a php function.
  This is working ok.  What I'd like to do is prevent a user from spamming the button.<br>
  At first I thought of maybe getting the IP address, storing that in the database and then running a check.  Is there a better way?</p>