31946 Need Apache .htaccess Expert

Hey guys..... I have a script which I send POST data to with a form button, but now I have noticed another site is taking advantage of that & also POST'ing the info to my script so I want to stop them from doing that. I don't want to rely on checking the referrer either as this isn't always set so I was hoping there would be a 100% or close enough solution that could be implemented with some code in .htaccess. I have tried using the example in the attached file but that ends up blocking everything, even my own site for some reason. I also tried using the apache directory directive but I always end up getting a 500 internal server error when I use that?? I need this done urgently, so please state when you can be online to do this with your bid & you also MUST have an instant messenger we can talk on. Thanks!