Awesome black powder story! Love it! Gophers are like miniature ground hogs, like 4-6" long. They make little tunnels all over the yard with waste dirt piles everywhere. Super annoying. Black is a favorite to use but I doubt it'll kill them unless maybe they're right there in it? but it's very satisfying. I have a bunch of waterproof fuse so i can put the powder way down deep with the fuse, bury it and stomp on it, lite and wait. You hear a dull thump and ~a square meter of dirt/lawn rises a bit and falls, then that same area smokes fera bit. The store bought smoke bombs suck, probably some bs legal limitation. Home brew work, just kinda a pain to make.
Then there's CO generators where people will will take an old whatever engine and run it cold n rich to make CO and pump the exhaust into the hole(s). I guess that works best but it takes all the fun out.
Are you saying you had no Gray squirrels on the island before this? I'm having trouble believing that choice squirrel territory existed for millions of years and they never found a way out there... Well, at least since the last ice age, but still. Interesting... Then of course man no doubt screwed that up, like we did to Hawaii, New Zealand and the idiot that brought rabbits to AU. Agent Smith in the Matrix said it best; "You humans are a virus."
Good ideal about having someone else print targets since they charge by the sheet, not the ink. I believe I suddenly need to print out a ton of "important" documents at work