If that was my Gundog Trainer I would have not returned and quickly found myself another one, no need at all to be aggressive with the dog
Try putting a noose around the trainers neck and giving it a good yank, I bet he would not approve.
I have learnt from my mistakes, I had my Springer in residential training with a very well known award winning trainer for over 4 months at some cost, first time I let him off the lead he ran off and I thought I had lost him, he returned 1 hr later as though nothing had happened, his recall was 0%, I have now changed trainers, started again from basics and my Springer is a totally different dog, not 100% we are both still learning but we will be getting there !!!