I have also used the "lay off a few hundred rounds of ammo" method to help deter trespassers/neighbor issues, and I've found it to be quite helpful.

As some of the recent posts have indicated, I agree that showing your neighbor some of the other options that he could be faced with as opposed to fishing may be a reasonable approach (jet skiing, target practice, etc.).

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."