This is another one of those things that you have to be sooooo consistent with (like coins in the can for barking!) but say 'no bite' or whatever you want to use and put something they are allowed to bit in front of their nose. They should be taught bite inhibition by their parents and litter mates, but sometimes this gets missed if they get separated too early (ask me how I know
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I also do the quick fingers at the neck, ala Cesar, but be very careful with this and the tiny ones.
But Purl is learning lots about 'no bite' from her big sis, cockapoo Lacey!!