im sure that would look awesome when done,id recommend using foam sheets from home depot and cutting out fake rock patterns of foam and siliconing them on than using a concrete mix......there vids on youtube of how to,as far as mixing goes most people will tell you no,i dont know much about canyon tree frogs or which geckos you plan on putting in there,you may be able to get away with it if the frog and gecko are the same size but it doesnt guarantee anything,im sure the fish will be ok as long as there tetras/mollys or something smaller.....good luck post pics!