LOL, the request makes me think of the bat scene in the movie "The Great Outdoors" with John Candy and Dan Akroyd.

Bats should be real sensitive to ultrasound deterrents. If it were me, I'd build my old trusty dog blaster, which used 3 40 watt piezo horns driven by an amp running a sweep gen from 15K to 25 Khz.

You should be able to find something similar (but less effective) on the net. Try and find something that pulses, because continuous signal would probably prevent them from being able to fly to escape.

The alternative would be a wire handled fly swatter???