Keep them like Budgett's Frog but with a small land area so they can leave the water if they wish.

A quick google came up with this site in German and it seems sound. I've put it in the translator for you:

Google Translate

If you've further questions, have a look at this and see if you can talk to this fellow:

http://www.frogforum.net/aquatic-cla...ging-eyes.html