I received an odd request from my manager recently. He wants to know
if we can warn users who click links that lead to external sites that
they are leaving our site. I am arguing against this on several
grounds, but want to understand all the technical possibilies. I
inherited the site and it is 90% static HTML with some PHP and Perl
applications.

I can think of a few ways to do this:

1. add a javascript onclick() event handler to each link to create a
popup.
2. pass the destination of each link to page that displays a warning,
then redirects the user to the destination.

Is there some obscure global apache setting that lets you trap a
clicked link and send a warning first?

What is the best and easiest way to do this?

TIA for any suggestions.