Create an onclick trigger on your button which includes some javascript [...]] Should do the trick.

Nope. Adding Javascript to the client will never solve a server side problem. Simply because Javascript is not always available on the client (LWP, WWW::Mechnanize, NoScript, filtering proxies, ...). And, quite obviously, it can be disabled on the client. In a WWW environment, you must not trust the client.

The server has to detect that the form was submitted several times. The usual approach is to give each form a unique ID (e.g. a UUID) in a hidden field or as part of the submit URL; and to make sure that each and every ID is accepted exactly once.

Alexander