[Koha] Exclude users from search (check out)

Hello, we use Koha in our school and therefor many students get enrolled each year, but also many students leave the school every year. Every year we have more and more users, that are not at school anymore, but they still exist in Koha. If we want to checkout books and search for the right user we have many similar names over the years, sometimes the same firstname and lastname. Is it possible to deactivate users so they are excluded from the search result (checkout)? I don't want to delete them because we will loose the circulation data. Regards, Stephan