The solution is very simple. Create a robots.txt file and place it at the root of your web site (e.g. mysite.com/robots.txt) and put in the following disallow statement to prevent this path from being spidered:
User-Agent: *
Disallow: /yoast-ga/
This allows you to continue tracking those external links and prevents the 404s you’re seeing in Google Webmaster Tools. Need more info about robots.txt? https://www.robotstxt.org/robotstxt.html
