Avoid crawling part of a page with "googleoff" and "googleon"

I am trying to tell Google and other search engines not to crawl some parts of my web page.

What I do is:

<!--googleoff: all-->

<select name="ddlCountry" id="ddlCountry">
<option value="All">All</option>
<option value="bahrain">Bahrain</option>
<option value="china">China</option>
</select>

<!--googleon: all-->

After I uploaded the page, I noticed that search engines are stilling rendering elements within the googleoff markup.

Am I doing something wrong?