When a dog guards a resource, animate or inanimate, they are responding to a perceived existential threat. We get offended when a dog guards a food bowl, toy, location, person or other animal and we make the situation worse, escalating the threat. Adding any kind of pain stimulation, or threat of pain or injury, can make the situation even more dangerous.
Novices, whether the public or many dog trainers (regardless of how long they have been in business), don’t see it from the dog’s perspective.
Let’s do it then from a human perspective. If someone came along and forcefully removed your clothing, or dragged you out of your car or home, or stole your purse, you’d naturally defend those resources.
It is the same reason why they used to hang people who stole horses or cattle. Steal the cattle and someone starves. Steal their horse, and they could very well starve, get injured, or succumb to the predations of other animals or people. That’s why people wore guns in the old West, and why people carry weapons and learn other ways of self defense today. In some circumstances you are your own first responder. You’d also act differently amid a war zone if someone tried to take your food bowl, risking the starvation of you or your family. You’d fight back.
So, give these dogs a break. Quit fighting with them. There are ways to deal with this humanely. If the situation is dangerous, don’t try to solve it yourself.
Plan accordingly.