Shoutbox

Ok. I have a contact form on my site, and have a JavaScript code to stop multiple submitting in one go. However, recently I have been getting lots and I think it may be because people have JavaScript turned off in their browser. I was talking to a friend this morning, and he said that the same effect could be done using php, and that it is more secure and reliable.

So:

a) Is this true

b) If so, how can I go about implementing it on my site??

Thanks in advance.