How to stop spammers entering http into a form to database

I have a form that sends info into a database table. I have it checked with a Javascript but what is the best way to stop spammers entering http and such into the database with PHP when Javascript is turned off?

Solution

You could implement a CAPTCHA on the form:

http://en.wikipedia.org/wiki/CAPTCHA

Edit: Also definitely verify form data on the server side and check for html tags etc as usual, but the CAPTCHA should help against automated spam attacks.