Things that tighten around the neck and jerking have led to neck problems and thyroid problems, that is why I suggest a harness. If he's pulling that hard, he could be doing real damage to his neck area.
For clicker training, check out
http://www.clickertraining.com/
http://www.clickertrain.com/whatis.html
And I would check out kikopup on youtube. She has videos on what clicker training is and how to do it. I've spent hours just typing clicker training in and watching videos.
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