I personally would consider changes along these lines :

Option A) Better saves on it, only usuable during pk (or optionally, also when fighting mobs who are ranked higher than level 51 or significantly more higher level then the person fighting them like lets say 10 levels higher). Likewise, warcry should improve morale if it doesn't already. In this manner, you use it when you need it most rather than shouting it because you have a free command to do so.

Option B) Make it callable like it is now, but also allow it to be called for a while after a pk. This way, if you flee or your opponent flees, you can call it while still in the 'thick of things'.

Option C) Make it callable when anyone who has previously killed you or you previously killed them is in the area or within your scan list.

Option D) Shout it automatically when you or your pk foe gets to 50% health, whichever comes first.

Just some options, on my warrior types when I see a necro coming I tend to remove my weapon, attack a nearby mob and call it so that I have it up prior to getting slept. Honestly that doesn't seem to make much sense to me at least.