While I have not kept darts, I have setup multiple vivariums for reptiles and other amphibians. but I will do a horizontal if a vertical will not work. And I said the wood is toxic when green. dry, it is used as bowls for pipes, and if there are any toxins left, burning should release them. so I think it should be safe. Is there anyone here who has kept a large viv. with a pair of frogs and have them breed and rear young without intervention? (artificial incubation, etc)? just was curious about that.