Fountain to deter frogs??? HAHA I have never hear that. My pond has 3 features moving water. This includes a large waterfall, a statuary spitter, and a small fountain. When used in conjunction they provide water movement throughout my pond. Yet, I get well over 1,000 tadpoles each year. The majority are toads but the tree fogs love it as well. And the pond is next to our bedroom window so we hear their mating calls at all hours of the night.
I would love to deter them as well once they drop a few tadpoles into the water but I have not found any method of doing so, short of getting a cat to hunt them down.
With that being said the best year I ever had was when a pair of leopard frogs made my pond their home. Their aggressive behavior pushed out the toads and tree frogs out of the area so we only had to deal with their mating calls which are much quieter and soothing than green tree frog screams and toads croaking.
In summary fountains will not work based on my experience, and the only suggestion I have is to research aggressive native frog species and try to introduce them to your pond to chase out the current population. Just ensure whatever species you introduce is not worse than the last as far as sound and diet, if it happens to include fish.