Dog Whistle is easy way to train your dog.
Use certain frequency when he do something bad, another frequency when he do something good.
You can teach him new tricks, with using diferent frequency.
Dog whistle have remote controler to set 8 frequences in range 5-22 kHz

Just tap on one of the button to save frequency. To reset it, just long click on it.
Dog Whistle is free app, very intuitive and easy to use.