None. Species mixing is a terrible idea in general, and if you add frogs to your geckos enclosure, they both will be stressed by it. illness and morbidity in amphibs can be directly linked to their stress level, and any frogs will be stressed living with the gecko in such tight quarters. The gecko won't be too pleased, either. Think of it this way, lets say you put them together, and they are horribly stressed by the others presence but they eat and move so you assume that all is well. Then your frog gets an injury that it could normally bounce back from. But since your frog is so stressed, it's immune system can't handle it and the animal succumbs to an otherwise minor ailment. What will you do? Spend more money and replace the frog, only leaving the other to suffer the same fate? There are some frogs that are stressed by the mere presence of a human in the room, much less another animal in the enclosure. The smaller, more delicate frogs wouldn't last long, and the more hearty ones would bully the gecko. It's not worth it in the end. Plus, its more rewarding to set up multiple species specific enclosures in my opinion. At least that way the animal is assured the best care.
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*~~Whitney~~*
Though here at journey's end I lie in darkness buried deep, beyond all towers strong and high, beyond all mountains steep, above all shadows rides the Sun and Stars forever dwell: I will not say the Day is done, nor bid the Stars farewell."