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.