You can integrate the DuckDuckGo search box to search your site using this wizard. There's a great writeup on how to change the style of that box over here.

If you'd like to add a handy search box that simply searches DuckDuckGo through your page, you can add this code to your site:

<form method="get" action="https://duckduckgo.com/">
    <input size="40" name="q">
    <input type="submit" value="Search">
</form>

If you have other needs or integration ideas, please let us know!