In zombie defense, I'd need a tool, not a fighting knife, because I'd need something with which I to fashion a wooden spear (a machete, hatchet, or an SAK with a saw in a pinch). I just don't understand why there aren't more characters in The Walking Dead carrying sharpened sticks, short lances, spears, or the like (only two regulars, really). I'm a big fan of the Maori taiaha as it can bludgeon, spear, and even cut one's opponent while being very portable on foot (unlike a long lance or a pike). I don't want to be in arm's reach of a zombie, and if I'm not shooting a bad guy, I don't want him near me. I suppose if I have to use a knife on a zombie, then, it would be a long bayonet on the end of a long gun. M1905 bayonet on my M1, M1907 on my SMLE, M1917 on my M1897 or Mossberg 500 (yeah, I put a heat shield/bayo lug on one of my M500 barrels).
Remember that for millennia the primary weapon of a soldier was the spear, halberd, bill, glaive, or (when mounted) lance. Even the samurai preferred the bow in their early years and continued to use the naginata and yari in battle. The sword has almost always been the sidearm. The knife is a tool and at most a sidearm, for eating and building and only as a last ditch weapon. Why? Because you just don't want anyone intent on doing you harm getting close.
Here endeth the lesson.
Zieg