I've had them spawn in a leaky Rubbermaid water trough turned upside down with a roughly 1 foot diameter hole cut in one end. They are currently spawning in structure that includes tires (triangles and groups of thee tied together side by side), concrete tiles about 2 feet in diameter, and a big 6 foot diameter concrete tile filled with about a dozen Osage Orange fence posts - I do not know which of these structures they are spawning in.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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