Question
I have a small pond & waterfall w way tooo many frogs for my liking.  They are small tree frogs w very large voices & the racket is ruining using our enjoyment.
I've tried cups of rock salt to no avail.....don't know if I'm not adding enough(4c to 350gallons) or whether it even works.
Please help before I'm eaten alive or taken to court for nuisance

Answer
Tree frogs will only come to the pond during breeding season.  So, first realize this won't last forever.  I know they are loud!  This time of the year, in the Eastern US, it's the spring peepers calling.  If you can identify the species, we can determine exactly how long it will last.

Does the pond have any fish?  If not, add some small fish.  Tree frogs almost never spawn in ponds with fish because they know the fish will eat their eggs.

Frogs are not doing well thanks to us humans.  So, please give them a break.  If you really want to not have them at all, you'll have to empty the pond.  Adding salt to the water won't harm them unless you add so much that it's toxic to all plants and animals.

I have a small page on deterring frogs at
http://www.fishpondinfo.com/frogs/frogdeter.htm

I hope they move on soon and that you treat them well until they do.  Good luck!