I have small unglazed terra cotta pots from Michael's Craft Store (my avatar photo)

I also have silk plants (not plastic)

I also have a black cave made by Fluval Click here It's small and my frogs love it.

I also have an Underwater Galleries AUG5402 Sea Cave, Small Click here Looks nice, they loved it, but I could not see them as easily so I removed it. If I had a larger tank though I probably would use it again but the black cave takes up less room in my tank.

They are all pretty smooth but I did check them. I also soaked them in prime treated water for a few days (changing water every day). If I felt any rough spots I used a dremmel to smooth them out. Same with the hole in the terracotta pot. I also fit the hole in the pot with a tight fitting piece of gravel to be on the safe side so as not to get their head stuck.