Install Bruteblock

 cd /usr/ports/security/bruteblock; make && make install

Configure Bruteblock

 vi /usr/local/etc/bruteblock/ssh.conf

Add line similar to following example according to your log in auth.log
also you can use line below for commercial SSH
OR
the line already in your current setting is good enough for standard installation.

 regexp2         = sshd2.*connection from \"(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\"

Change max_count to

 max_count       = 10   (10 tries)

Change within_time to

 within_time     = 45   (within 45 second)

Change reset_ip to

 reset_ip       = 3600  (Block for 1 Hr.)

Enable bruteblock to the rc.conf

bruteblockd_enable="YES"
bruteblockd_table="1"
bruteblockd_flags="-s 60"

Add following line to /etc/firewall as second entry after flush or you can edit your standard firewall rule file

 add deny ip from table(1) to any

Apply the changes

 ipfw -f /etc/firewall

Add following line to /etc/syslog.conf

 auth.info;authpriv.info                         |exec /usr/local/sbin/bruteblock -f /usr/local/etc/bruteblock/ssh.conf

restart syslogd

 /etc/rc.d/syslogd restart

start bruteblockd

 /usr/local/etc/rc.d/bruteblockd.sh start

How to check blocked IP

 ipfw table 1 list

How to flush table

 ipfw table 1 flush

Anything else in mind - GOOGLE it

This will help you keep you server live during any DDOS or bruteforce.
also, make person frustrated due to slow scan.

ipfw add allow tcp from xx.xx.xx.xx/24 to any setup limit src-addr 10
ipfw add allow tcp from any to me setup limit src-addr 4 

NOTE : First rule is for your internal network. replace xx.xx.xx.xx your internal network.