This question is not about how to protect the default search engine in Chrome (which is, unfortunately, the only advice I can find when I try to search for the answer to this).
I use and edit the full list of Chrome search engines regularly:
When I go to the list, there are usually many search engines added for sites that I have visited, but have not added to the list, and I regularly have to clean this list out. I don't know if the site is adding itself to the list or if Chrome is making some executive decision for me for sites that I visit regularly, but I'd like to keep it from happening.
Is there a way to only allow manual additions to the search engines list?