Just tossing it on here for reference - detailed info on proc rates from recent blue post:
Fangs of the Father
Assassination: 23.139% chance on white/yellow melee landing, no ICD.
Combat: 9.438% chance on white/yellow melee landing, no ICD.
Subtlety: 28.223% chance on white/yellow melee landing, no ICD.
These chances are multiplied by 0.9 for lvl 89 targets, 0.8 for lvl 90 targets, 0.7 for lvl 91 targets, 0.6 for lvl 92 targets, and 0.5 for lvl 93+ targets.
After adding a stack, if you have >30 stacks, you have a [1/(51-stacks)] chance to proc the Fury buff.
http://us.battle.net/wow/en/forum/to...36?page=14#261