Filter by IP - We can set up a firewall to filter SSH access to the SSH port by IP.
Change SSH Port - This doesn't prevent access, it just changes the port of access.
Use /etc/hosts.deny and /etc/hosts.allow - Utilize application/system level access settings for access to system services.
Use SSH RSA Keys - Disable password/keyboard-interactive authentication and only allow key access.
We can enable 1 or all options at any time.