Those who've added a morale rule for adversaries to your Whitehack game, what rule are you using?

Those who've added a morale rule for adversaries to your Whitehack game, what rule are you using? Something cadged from D&D? An extension of an existing Whitehack rule? Something of your own devise?

And how has this rule worked out for you in play?

I realize there's a morale rule for hirelings on p29 (let the PC with the affiliation for those hirelings check Cha). I'm curious about morale for monsters.

Thanks in advance!