What I use and how I do it.
When my dog is itchy she rubs herself or bites the itch, and males get it more intence, they get it inside and out. What I use is called Grannick's Bitter Apple it is in a yellow plastic pump bottle from the pet department at Peavey Mart.
I spray it on the itchy part of the dog, even the least red parts. Make sure you spray all the touchy areas underneath there as it usually starts under the tail and spreads down under the tummy. Dr called it Heat Rash, like a baby gets a diaper rash in hot weather. They bite themselves a lot too and this helps to stop the itch there too. You must wash your hands after rubbing it into his skin. Take my word they don't like the taste of it and will leave it alone after a few tastes, and let it do the job on the irritation. Good Luck God Bless you and your dog.