Currently, whenever a DOS or password brute force attempts are detected, the offending IP by protocol are temporary blocked (or blacklisted) for the specified minutes in "Time to Block."

 

Are you wanting an option to permanently add the IP to the blacklist?

 

I will add this to our feature request list for further consideration with the dev team.  As for the "Time to Block" setting, it is under System Admin -> Security -> Advanced Settings -> Abuse Detection. All of the abuse detection types have that field available.