Later this year I will be teaching classes on 'tanto tori' - defences against knife attacks. We will practise with wooden knives for safety. I've always found tanto defences one of the most challenging and interesting aspects of aikido. At black belt level you are expected to be able to perform these defences against real knives, so you need to have both the technical skill and also (just as important!) the calmness of mind to deal with whatever happens to come your way. Many years ago, when I used to practise with my teacher, Sensei David Currie, I undertook quite a long series of private lessons in which we explored defences against all kinds of weapons - from baseball bats to broken bottles.
Fear not! We won't be using any of those somewhat unconventional weapons in the Hartland club. We'll stick strictly to the wooden tantos. Here is a short video I came across of some basic tanto defences. Incidentally, this teacher (Mike Jones of the New York Aikikai) has a number of videos on YouTube. I recommend them. They are well filmed and Mike Jones is a very clear and engaging teacher.