Display random url for actual download link url

I will be implementing a "pay with a facebook like" "pay with a tweet" "pay with a GPlus" on a php webpage, where the user must click either a FBook Like, Twitter or GPlus icon to "like", "tweet" or "+" about the website before they are granted permission to download a file. As soon as they do one of the three, then he file download begins straight away. To make the job easier I have found some code online done in Javascript. (although I haven't tested it yet, user comments say that it works fine). However, in this javascript code, when the user's download of the file begins they will be able to see the url of the download file, and also in the page source code. I need some code made in addition to this to show a "random" url for the download file location. If ever someone tries to access this random url in another browser or session later on, it will not work, it will simply go to my website 404 page. I suppose some htacess and possibly cookie session coding may need to be done for this. I don't mind which other coding language is used to create the randomized code, either php, java, cgi, whatever will work is fine. In private message I can show you the existing code I have made in javascript. If you have any questions, feel free to ask to clarify before proceeding. Thanks for reading.