Patrick Stox is a technical SEO consultant who writes for Search Engine Land and speaks at conferences. He discusses various tools and techniques for investigating a drop in search traffic, including checking for changes to content, tags, redirects, links, and what Google is seeing versus users. Some issues that could cause problems are things not working together like blocking crawling or noindexing pages, multiple conflicting tags, or rules that redirect Googlebot differently than users. The key is to thoroughly examine all possible areas that could have changed using various Google Search and other SEO tools.