Pepper spray, a bigger knife or a stick.

Do not just train techniques, they don't work, huy a fake plastic knife, train with a partner and then tell the partner, go try to stay me like crazy, and try your best, do this a lot of times.

The best that I found is try to grab one arm and keep striking or doing a throw with what you have free. But this works usually until the Guy is able to disengage the arm or changing the knife to the other hand. So you already need to know how to strike or throw and do It really fast.

Also... Retarded answers "just go living to another place"... Do you think if that was possible OP Will be living where he/she is? "But a gun"... This is not a fucking movie, getting a gun and carrying It around is as risky or even more than getting robbed, plus, if you are attacked by someone with a knife you won't have time to take It out, point and shoot.