Hide Custom Page from Search Engines

I've created a .html page with a few assets and uploaded them via FTP to my website. I named the .html page index.html and put it in the directory /directoryName, so that I can go to mydomain.com/directoryName (without .html extension) to see page.

This is one of the rare occasions that I will be doing this. I have used the META NOFOLLOW and NOINDEX attributes to prevent search engines from crawling this page. What are some other methods of preventing search engines from crawling/indexing the directory without interfering with WordPress installation (that's entire rest of site, this is only instance of such setup)? Note that this is the only directory that I want to be affected by these code additions.

Maybe some .htaccess solutions or something else? Not really sure, could some staff members provide suggestions here. I know there is no definite way of blocking search engines, but just trying best.

Please respond ASAP. Thanks in advance!