I had them in a ground level tub close to the pond. I kept a screen over it to keep cats or whatever out. I had a few rocks on the screen too. I left room so a mature tadpole could exit and find the pond.
I would notice the screen moved twice, just a bit. Turns out there was one well developed tadpole remaining. Either a critter got them, or they went to the pond, I hope.
I put the last one in. Fingers crossed, but not confident :'( :'(