Anti Dog Barking circuit amp and speaker

I am having a major problem with a dog barking next door at all times of the day and night. I have tried an off the shelf device and this has not worked. I am now building a new circuit which I hope has uploaded to this post. I have 2 questions:
1) How can I increase the power output
2) WHat is the best speaker/sounder to use to produce the loudes ultrasonic sound?

Many thanks all.

If you make an ultrasonic noise then the dog might bark at it.
A piezo tweeter might do it.

The device would only emit a sound in response to the dog barking. The theory is that it conditions the dog and stops the barking. The frequency would need to be 20-30KHz and I was thinking about a Piezzo tweeter but see the output decreases sharply above 20KHz. Any other ideas?