English is below.
I never met griefers in private server but would like you to make a hedge against them. So, could you disable banishment voting except an owner and inhibit a griefer from playing in a server if ones an owner voted the griefer?
I changed your title so that people wouldnt just glance over it
The permanent part will let people know that its not just making it so only owners can banish and imply that the owners could pemanently ban someone.