I love Tachy Goes To Coventry and have used it many times as an effective tool for thwarting a member who insists on being part of the community.
Basically they are allowed to join and rant to their hearts content, but no other member has to deal with them. When somebody gets sent to Coventry, it usually takes them days or weeks to figure out that they are being ignored. In that respect, sending them to Coventry gets them off your back for longer than a brute-force banning.
I agree that for the most part keeping a determined user off your board is going to come down to a test of endurance between the user and you and your Mod team. My Mod team loves this particular game and so not too much gets past them.