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Ultrasonic Speaker

I have several neighbor dogs that bark,and would like to make some cheap dog barker busters.

The first half of the project would be to create cheap ultrasonic speakers.  The second half would be to create a bark activation circuit.

Part 1

I'm thinking about modifying the dollar store perimeter alarm linked below: 

the diagram for the circuit is pretty simple, and mostly matches:

to change the frequency of the oscillations, it is necessary to change the capacitance of the capacitor.

here is a chart of capacitance to hertz tones, though it is not helpful for the ultrasonic range i am looking for:

I have a couple barker breakers, i am going to disassemble one and check the capacitors on that to give me an idea of what I am looking for in a capacitor.  After that, it should be just a swap of capacitor to push the alarm into ultrasonic hertz (though the speaker might not work well with it).