In regards to keeping him away from potential opponents, I can totally understand that reasoning but the cap cost just isn't worth it. If you are hellbent on keeping an elite QB away from your immediate competition, a better solution would be to pick up said elite QB in the draft and trade him away to a team in the opposite conference from you, preferably to a team with both a crappy offensive coordinator and playbook. You'd still be making out pretty good as you'd likely get a couple high picks or an elite player in return for the trade.