I think the bitter taste method is probably one of the best ways for a "nippy" ferret, but 70% of it is not to fear your ferret in the first place, look at the size of a ferret, even a big hob, sure when they bite it hurts,but no more than wacking your thumb with a hammer or kneeling on a hawthorn, it aint gonna be life threatening, so be brave,be confident, and use the vinegar to make sure you taste like shite, should soon have a well behaved stinker.