One of the easiest things you can do to help reduce the hammering on your management services such as HTTP and SSH, is to change the port. While this is not really a way of securing these services, it does provide a little bit of a buffer from scanning bots.

  set service ssh port 8022
  set service gui https-port 8443

The real way of securing these services is to firewall them off with ACLs so that only trusted IPs can connect to them.