After having noticed that there isn't really anything preventing an air elemental from knocking you down for about 10 minutes straight, I was wondering if it would be difficult at all to place maybe a 15 second cooldown on the knockdown effect, similar to the cooldown for trip, so that characters that can't kill them from afar via FoD, PK, Destruction, or the like will at least have a shot at killing them in a timely manner. That or perhaps the DC could be slightly lowered.
Just a minor suggestion.