How to prevent multiple form submissions

GRRRR!!
I have 1 pain in the butt user who continuously fills a form with garbage.
I am constantly cleaning the user from my data base.
How can I prevent multiple form submissions? Will a cookie work to prevent user from multiple form submissions for longer than a session?
If not cookies, php code?

Can I authenticate the email listed in the form, not just the structure?

I have looked online but I cant make sense of the code and where to place it.
My pages wont display as there are errors when code is inserted.
Thanks
David B

does your form save the information to a database?

if so, add a column to the table to store the users IP address. in the insert behavior, bind the new IP column to the REMOTE_ADDR binding from the server collection.

once you know the IP address of the problem user, you can ban them using PHP on your site, seer the following page for details:
how-to-block-ip-addresses-with-php/

Thanks for that, got the url in my data base.
How do I get and store the username of the user (user not logged in)
I could also store this on my data base in conjunction with the ip address.
Thanks
David

  How do I get and store the username of the user (user not logged in)  

is the username one of the fields in the form?

if so you can get the username from the form. but you are relying on the person filling in the form to enter the correct username.

if it is not a part of the form, then there is not a way to get the username if they are not logged in.