I know there is a such a button for council members but why not for kings, whose death has a lot bigger impact on the game? The only way to do it is to select him as a general and press resign every single time you raise troops, so it gets tiresome and repetitive quickly and if you forget about it, you're king is now dead. I know it's historical for kings to lead troops but people just resign them anyways, it can be complete and utterly devastating to have your ruler die when you're the head a of a large empire.