I just use the "Gentle" command here, and it's worked great for my cats and dogs.

I hold out a little peice between my fingers, really only enough so they can smell it and lick it at first, if they chomp down I will say "Ouch" in a kind of yelping way.

Then we will try again, I say "Gentle" in a soft voice, they generally get it right the second time around and then never have a problem again.

Hope everything continues to go well for you 2