Cookie to stop users from using multiple accounts on my forum

[Redux]

I'm writing a PHP script for a forum I use.
When a user is temporarily banned from posting on the forum, it is designed to set a cookie that will disallow other users (or alternate accounts) from posting on the machine that the original user was banned on.

However, I've hit a bit of a snag. The user could close their browser, clear cookies and create another account, and the script wouldn't be any the wiser.

Is there any way I could prevent users from deleting the cookie and making a new account?

[Termana]

no, there is no way to stop a cookie from being deleted.
Posted via CodeCall Mobile

[Jordan]

Exactly as Termana said. Even if the browser could be told not to delete it (which could easily be used for malicious intent), cookies are stored as a file and could be deleted by anyone that knows where they are store.

Why not use the IP address? Or better yet, use the MAC address (although you would need to fetch it using JavaScript)?