Finding HTML

I'm about to undergo a creation of a Link Exchange script for my site. One of the requirements is to have them have my button on their site in return for a button on mine. This is required and I don't want cheating. The only way I can think of doing this is checking their source code and making sure the code is still intact on their website about once a month. If not, then their button is removed from my site. Instead of doing this manually, I want to do it in PHP. This brings me to my question. How can I, without using FTP since I don't collect usernames or passwords, check their source code for my block of code? Then if it's not there, delete their entry from a table in MySQL? Any help would be great. Thanks, Stephen Craton http://www.melchior.us "Life is a gift from God. Wasting it is like destroying your favorite item you received from the person you love most." -- www.melchior.us