I bet very few cities and counties in Nebraska have any mention of metal detecting in their city or county codes, laws, and/or rules. It's not something that's usually ever addressed on those levels. And if there's no prohibitions, presto, there's your answer: It's not prohibited. If you're skittish and wonder, then do as lady-pirate says: you can look up the laws for yourself. City laws, charters, muni-codes, etc... are often times on the city website. Or at a minimum, down at city hall in binder form for public viewing. If you see nothing there saying anything about detecting, presto, there's your answer. Look it up yourself, rather than asking some desk-bound person "can I metal detect?". Because you don't want to get someone to say "no", when no rule really exists, that says such a thing (simply because they're in a bad mood, or think you might harm earthworms, etc...).
And then wherever you go, still use due-discretion on timing. Avoid busy-body lookie-lous, since, afterall, detecting has connotations. So go at low traffic times. And naturally, avoid obvious historic sacred monuments, lest someone get their panties in knot. Don't go waltzing over beach blankets at an archie convention, etc.... But for run-of-the-mill city parks, sandboxes, beaches, I never hesitate to hunt wherever I travel to.
