Force no cache for unregistered users
You can turn off caching by going to Configuration > Performance, and uncheck "Cache pages for anonymous users."  That will turn off page caching for the whole site.

If you only want to keep specific pages from being cached you can use Cache Exclude.

You can also (but it is not recommended; see the comments) enter this PHP snippet into the page's template, for example node--123.tpl.php.

// Keep the page from being cached
$GLOBALS['conf']['cache'] = FALSE;