There needs to be a popup with an "I agree" button before you make your first post on GD.

Most of the necros are because people Google search something, find a thread (which happens to be on GD), and then make their first post in months (or first post ever), necroing the thread because things on GD get "bumped" and things on other boards don't.

A simple disclaimer before your first post (a popup) "General Discussion is a chronological view like any other normal forum. Please don't bump old threads. You may be banned." with an "I agree" button would probably stop this from happening.