Pet Whistles

I am wanting to redesign and make improvements on two types of dog training whistles, one is metal and one is plastic. The metal one has an adjustable screw that works its way loose, so I want to design this screw in order for it to still be adjustable, but unable to fall out from the whistle part. The plastic whistle I want to change the frequency in order for it to be almost silent and I want ideas on redesigning as the original I believe is patented.