you can simply add a line in your .htaccess like this
ErrorDocument 404
http://adultpornos.net/
or to redirect basic errors do all these 400's and 500 as I do
ErrorDocument 400
http://adultpornos.net/
ErrorDocument 401
http://adultpornos.net/
ErrorDocument 403
http://adultpornos.net/
ErrorDocument 404
http://adultpornos.net/
ErrorDocument 500
http://adultpornos.net/
another thing you can do is set this to stop anyone from seeing the files in directories with no default page is to add this
Options -Indexes
the minus sign means simply not to show indexes of the files in the subdirectories