For the post to be removed you would be best to add a disallow to your robots.txt file
Then submit another removal request.
The reason the page is coming up in Webmaster Tools will probably be because Googlebot is following an external link - if you log in to Webmaster Tools the page will more than likely be in the 404 error report. you can check where Google is getting the location of the page with the 'linked from' tab.
The page will disappear in its own time if it returns a 404 error, but if you disallow it in robots.txt and submit a new removal request then it will be gone for good.
Just to add an edit (I can't add a comment)
From the Webmaster Tools URL removal page: https://support.google.com/webmasters/answer/1663419
If the page no longer exists, make sure that the server returns a 404 (Not Found) or 410 (Gone) HTTP status code. Non-HTML file (like PDFs) should be completely removed from your server.
If the page still exists, use robots.txt to prevent Google from crawling it. Even if a URL is disallowed by robots.txt we may still index the page if we find its URL on another site. However, we won't index the page if it's blocked in robots.txt and there is an active URL removal request for the page.
So it looks like the only 'tidy' solution is to just let it 404 for a while.