Changing "Search Here…" text in search bar

I am developing a site for a customer using the responsive theme from Cyber Chimps and would like to be able to change the “Search Here… “which appears in the search bar. I know I can change it in searchform.php. However, when I am gone and my client does a software update they will lose that change as searchform.php will most likely be replaced in the update. I would like to use my child theme to do this. Does anybody have any ideas?