Hi
@Ben, welcome to CF
Just to clarify - are you looking to block the site from appearing in search results i.e on a Google results page, or access to the site?
Blocking access to the site is usually the easiest approach to take.
You can also customise your search results when searching to exclude a site using the negative operator -
For example, the following query:
spl center -splcenter.org
Will retrieve results matching spl center but exclude ALL from the domain splcenter.org.