IMHO there is a misunderstanding in tanto dori training which seems to lead some people to believe they are learning to defend against knife attacks. Tantodori, like all weapons training in Aikido, is a broadening of understanding and experience with maai, as well as a sharpening of general awareness about body placing and control of uke. This could, under certain circiumstances, be taken further into self defense technique, but only by stepping away from telegraphed, no-feint, single classic attack style training. To imagine otherwise can be foolhardy and dangerous. I totally agree with other posters that against a trained knife fighter most of us would not survive, and I have some knife training experience. If you want to scare yourself a bit find an old keikogi and arm someone with a a red magic marker and ask them to attack you. Remember that stabs are not always needed, enough cuts and you simply bleed out, get caught on tendons and lose the use of the limb. Not everybody holds a knife the same way, so grabbing from the top can cost your hand. I would also recommend Hochstein, and also Ryan and Janich for study, and absolutely geta look at Kali. When you've done all that revisit basic training and start again. Good luck, and running fast after good distraction is still your best bet.