Slash McCoy
I freehand dog rockets
He hasn't sprouted much in the way of armpit hair. I just purchased some well regarded deodorant soap, haven't been able to find an alum block yet.
Try Whole Foods if you have one in your area. They have two brands: Crystal, and Thai Crystal. They are sold as deoderant but you can use them on your face as well. They are pretty much the same. Both brands are packaged as sticks in holders similar to conventional stick deoderant. Very convenient. A large block, good for a couple of years, for about $5. Most organic or health food stores will have one of these or another brand. I have never ran across alum block at walgreens or wallmart. Of course you can buy it online, too. I think you will find an alum block will make a tremendous difference. Other deoderants mostly mask odor behind their own often (to me) hideous odor. Alum block actually prevents odor from occurring in the first place by making a very inhospitable environment for the bacteria that cause it. Plus it leaves no scent of its own behind. I most highly recommend it for him and for yourself.
Another possible source is your local Indian or Middle Eastern grocery. It may be sold as shaving alum or as deoderant alum. Either one can be used for both purposes. It should be less than a buck at an Indian grocery. I just bought some for 54 cents for a 100g block.
There are actually two different chemicals sold as alum. Either will work so don't worry about which one you are getting.
To apply, just wet it and rub it on. Easy peasy.