Fail2ban is absolutely necessary for any Linux system, especially for Untangle.
`apt get fail2ban`
By default, have it set up a chain to block 4 or more failed ssh attempts. Run IPS with all rules enabled, but notice you will still receive attempts from China to port 22 because neither the layer 7 apps nor the IPS protect the untangle box itself.
Forbid password only attempts to port 22 over the wan connection.