There's already a few posts on here about htaccess – but here's one more.
Blocking linking URLs
Essentially the link above says this:
SetEnvIfNoCase Referer "^http://www.google.com/" BadReferrer
order deny,allow
deny from env=BadReferrer
That will forward anyone linking to your site to a 403 access denied error page.
RewriteEngine On
RewriteCond %{HTTP_REFERER} ^http://www.google.com/
RewriteRule /* http://www.yoursite.com/restricted_url.html [R,L]
That will forward anyone linking to your site to the http://www.yoursite.com/restricted_url.html page.