Hacco produces a restricted rat/gopher/squirrel poison called "Pro-Zap." It was zinc phosphide on groated oats.

Killed whatever ate it in about 15 minutes, with little secondary kill risk - a lot less secondary risk than the anticoagulant rat/vermin poisons out there.

Here's Hacco's rodentcide page:

http://www.hacco.com/Rodenticides.htm