Piezo sounders can be much louder than the ones used on Dazers and similar devices. They can be ultrasonic, or not.
Like LEDs, they can be purchased separately.
Some of them sound freaky. Like some otherworldly electronic bullfrog croaking, amplified greatly.
They make most dogs stop or turn around.
It would not be difficult to set up a bike with two or more of these mounted and wired, with a control switch on the bars. Sometimes dogs don't allow you much warning or time. Quick response is desirable. Hitting the switch and activating the sounders would be very quick.
If anyone tries, or has tried, something like this, please post; it would be interesting to see or read about.