There are several approaches for this:
1. Simply don't use WP
2. Search a WP hoster that has a "keep WP & theme & plugin up to date" service to always have the latest fixes live (though it doesn't prevent you of getting hacked before any fix of a security issue is published and installed)
3. There are some security plugins for WP available (though I don't like the idea to fix something insecure with adding some plugin)
4. There exists plugins that allow you to export your WP to static html files only. This is the most secure approach, but you will lose interactivity (blog comments, most of plugins not working anymore). But if you can live with that restriction, it's for sure the most secure thing to do.