I have this plugin which when someone clicks the X button to leave the page, a box appears and gives a message, and has two options, to stay or to leave. There is a global setting with a default url to redirect the ones who click 'stay', and there is a box where you put in the message you want to show up. There's also the option when adding the shortcode in the post to put a custom url, so that exit traffic from that post will go a different url than in the global setting. So what I'd like to know is, how can I rotate the urls and track them to see which one performs best for each post on my site? Any suggestions?