One - Would require you to download all your addon/data/lua files and get a free 24hCrident server, then you'd upload the downloaded files to the Crident FTP and use the "Backdoor scanner" service.
Two - I would recommend getting the "CPE" addon for gmod, (I would recommend doing both as CPE doesn't get everything.)
RE: Has your server been "Hacked" or "Backdoored"?
If i use both of these will i be guaranteed to get rid of all of the backdoors? i don't want any backdoors on because they can give other people owner?