SSHGuard is a service that automatically creates firewall rules to block the IP address of anyone trying to brute-force attack SSH on your server. IMO it is essential for any internet facing server.
Unfortunately there is a bug in the current version (1.7.1) in ports, which will prevent the service from starting on FreeBSD 11.0:
ipfw: failed to request table info: No such process
SSHGuard is trying to reference a ipfw lookup table which has not yet been created. To fix this bug you need create the table manually with:
/sbin/ipfw -q table 22 create
You should now be able to start the service.