I really don't like the idea of you using a real knife, much less a chef's knife. Was Darlie's knife 10"? I can't remember. You could use a shorter knife, maybe a duller one and make up the rest of the length with the marker. Or you could try to find a Halloween party knife. If you use a real knife, wrap the darn thing up well! I can see this hitting the news:
Crazed Lady In TX Attacks Daughter On The Advise Of Online Crazed Amateur Sleuths! To Husband's Horror, His Exspensive Chef's Knife Sustained Fatal Damage