Offline and pull based backups FTW... This is why I advocate for a pull or at least push/pull model for backups... where the remote system pulls backups out of your production environment, or otherwise from a drop point. Because a corrupt production system that controls backups can corrupt backups.

If your production system at most runs a backup to a drop site, then your backup facilities pull down versioned backups from there, you can better ensure older backup files are intact. More so by not allowing the two to see each other at all and not using backup accounts from a system that can access production resources.