Thank you Lazy badger for your link. As this not a specific "VisualSVN" talk I missed it when I was looking for an answer. This answer is a bit simpler than what I was expecting but it will do the trick.
So i'm answering myself :
Just turn to "off" the "SVNListParentPath" line in C:\Program Files (x86)\VisualSVN Server\conf\httpd.conf (default path).
Rather than the repositories listing, it will display a "forbidden" page.
I've also did something else : I've modified the "index.html" in C:\Program Files (x86)\VisualSVN Server\htdocs, to disable the automatic redirect to "/svn/" (first meta above body in the file) and to remove anything which tells there is SVN repositories behind the url.