I have always had amazing luck with conibear traps with woodchucks. Once they stick their head through they dont get a second chance to learn to avoid it next time they see it like they do with havahart traps.
got this sucker last year after it kept insisting on spreading dirt from under the pine into the grass. usually when there is one, theres a few more.
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The only downside is that theres always the possibility of catching a skunk... which yes I have accidentally got skunks before. im sure out by you, any good hardware should have them in stock. think duke brand and conibear brand are basically exactly the same. cant remember the number series size though but its roughly a 7x7" square. trick is to not get your hand caught in it when setting it, though there is a tool made for setting them if you cant squeeze the springs with your hands.. should be a simple fab at work to make one though.