Sounds like you're already pretty efficient with Sounds. Let me tell my thoughts on how Sound Genjutsu works, and how it can be countered.
Before we get into the task you asked me to do, let me tell you my thought on genjutsu (Because Biology I understand better than Physics xD). There's tree things that would stop a sound Genjutsu, and those are based on the process of getting a wave of sound (which carries your chakra) into your brain.
Firstly, blocking the wave, preventing it from reaching your years. This comes from the inherit characteristics of sound waves, so it's more of your area than mine. But basically, if you isolate your ears from the sound wave, it can't produce it's effects. Stopping the chakra itself, maybe through fuuin or some sort of barrier should work fine. In a very basic manner, this would be the method one employs when covering one's ears. But can be added further with Sound's natural weakness to Wind
Secondly, destroying the sound receptors in the ear. Without them, the wave can't be captured/sensed, and the info or the chakra isn't transported to the brain. I don't think just having waves hit the body work, because soung genjutsus are not about the physic properties of sound and how it reacts to matter as a whole, just the sensors in the ear. This is the method one employs when one tries to pierce one's hears with a needle of something similar.
Thirdly, mess with the brain itself. There's a syndrome called Agnosia, and a branch for sound reception. Basically there's two types of deafness, physical deafness, where you're unable to retrieve sound from the world (Second method, basically), and mental deafness, where you can retrieve sound from the exterior, but the area of your brain that translates it doesn't work, so the information can't be processed. People with sound agnosia can't be affected by sound genjutsu (or sound-based illusions). Someone proficient enough with genjutsu might be able to recreate agnosia. I even have a few jutsus that do just that xD
Note, this is about actual genjutsu, not symptoms like making your opponent's ears bleed.