Kapkao-One use I could think of, would be in the form of triphenylarsine (although I usually use the more prevalent, and cheaper, triphenylphosphine myself), for such things as inducing crystallization of difficult to crystallize things, arsenic finds use as a common n-type semiconductor dopant, as well as in laser crystals.
Plenty of other uses, chemical warfare agents (lewisite, and some of the vomit agents like adamsite and other chlorovinylarsine derivatives), pigments (napoleon is thought to have suffered arsenic toxicosis from arsine, evolved from the paris green, an arsenical pigment, in the wall paper), and the first successful drug to combat african typanosomiasis (sleeping sickness) was an organoarsenic derivative also.
How does define 'modern' in terms of hunting. semi-auto rifles? black powder muzzle-loading fossils?
And who really gives a stuff if its legal or not. If you are hungry, poaching puts food on the table (assuming you bag something while your out of course)
And heh...the day your scenario comes to pass rage, then it will no longer be rabbits I'm after poaching, but bigger, more..cerebral...game. Shit goes all post-apocalyptic, I reckon my..talents, would make for a pretty good insurgent haha.