My old jujutsu teacher (who taught defense against knifes, although not really effectively) used to say to us that the only good defense was a good time at 100m dash, since there was no winners in a knife fight, only different degree of losers. You WILL get cut.
I like the marker pen drill. just make sure to train is old jeans and cheap t-shirts that day.
As a alternative if you got the economy for it, there is also a shockknife available now. a knife with a weak but very noticeable electric current running down the "edge". A good tool for training defense against a knife. Not cheap though.
Shocknife - Home