@lcuk, we could have a regular: touch-to-scare-them-away control. Works on everything with touch, but is sooo common.
I'm thinking about jiggle-the-screen-to-attract-them. Force needed depends on the character of a sheep.

Then, we have a regular shepherd dog approach, that can be controlled with keyboard/screen control. In this case I have been playing with a new idea of on-screen control buttons for a while, it could be a nice test-field ( ). The cons is that it is not so casual as using accelerometers or even touch screen.

Maybe a hybrid solution?