I had an interesting incident in this realm with the "fishing Mafia" here in Japan.
Although I understand that in most places on the mainland is technically permitted, in practicality, all shoreline is controlled by the fisherman, which is a very powerful group here. They vigorously discourage diving anywhere but at designated "pay" dive sites.
One time on a pre-dawn diving raid with a friend, we tried a new "free" dive site. Toward the end of a slow ascent up a gentle incline of a the rocky bottom, I noticed that we were being silently buzzed by a small fishing boat, powered by a jet. I was amazed that I could not hear it at all, I had thougth that jet boats would be really loud underwater.
Anyway, this guy was following my bubbles as I was coming up the slope and trying to hit me with a bamboo pole. I became rather infuriated, and was trying to catch hold of the bamboo, as my maniacal plan was to pull him in and introduce him to the bottom for edification.
Never happened. When I surfaced, he yelled a bunch of stuff at me I didn't understand, and I retorted with a stream of obsenities that was no doubt greek to him as well. We both seemed satisfied with what we had said, and he went along his way...
JAG