His weakness (or one of them). He will work for micro-bites of cheese. Keeping them in my pocket in the summer might be a challenge. But, surprisingly, kibble works almost as well.
As for the prong collar - regardless of whether it is cruel, or works generally, it won't work if my daughter is unwilling to use it. So we need another method. My high school sweetheart (dog trainer and obedience judge) agrees with both of us - you that prong collars are effective and aren't inherently cruel - but also with me that the dog's owner has to be willing to use it without hesitation or it won't be an effective tool.
Fortunately - so far - a gentle touch seems to work with him. I've worked with him (I think) a dozen times. Just started today on outdoor obedience. I got him to sit and stay when there were dogs barking nearby, and kids making noise in the house we stopped in front of. He's not perfect yet - but he stayed to a count of 20 three times on our walk today. He's starting to get the hang of walking close to my side, rather than charging ahead at the end of whatever leash I give him.
The book looks interesting!