Put Raze back the way it use to be and allow it to Raze land during War again.
That single change would greatly cut back on the sheer number of Suiciders that are now currently in the game.
If they wish to suicide, with raze fixed in War allowing the destruction of land again would allow a kingdom to decimate them if they choose to suicide.
The way it currently is suiciders are not penalized and if you try to hit them numerous times, hit protection kicks in and it takes forever to bring them down.