I used fairly green Osage Orange in my terraria. I cut off the roots, power washed them (water only, no soap), and let them freeze outside in the cold weather--this is what I was told to do by the folks that work at Chicago's Shedd Aquarium.
They were in the terrarium for about 3 months before I added frogs, but my frogs have shown no adverse affects now over 1.5 years later (and the wood shows no sign of rot, either. Locust and white oak are both good choices, with locust probably the better of the two for water resistance. Be prepared to have your chainsaw sharpened when you finish; the Osage Orange really dulled my blades!
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Homer W. Faucett III, esq.
Purveyor of Trivialities and Fine Nonsense