How to be sure to use SSL

Hi, I would like to know how can i be sure to make customer use the SSL all the time. all the time in my PHP code, i write links as relative links, so without HTTPS. I was thinking to check everything if the port is the SSL port (default : 443), but it does not mean that protocol is HTTPS. So, how do you ensure that customer uses SSL protocol all the time ? thanks a lot, Alain ------------------------------------ Windows XP SP2 PostgreSQL 8.1.4 Apache 2.0.58 PHP 5