Storing backup safely

Hi,
I have question how do you store a backup. Scylla manager stores and deletes backup and has to have a secret key to the Storage in its configuration. What if someone unauthorised will have access to machine with that config and use secret key to delete the backups?
What solutions do you use?

how would someone get access to that machine? where is that machine?
can you please clarify where is your configuration/setup?