I agree, onewoman are you sure he's washing properly?
Then drying completely, then applying deo?
You need to pop into the shower room when he's in there to get towels or something, and mention it in passing. He should be washing in shower gel / soap under his arms and his hair too.
If his pits aren't washed with a good foam of soap and rinsed, and then not dried properly, the deo won't work. Get him to dry with a hair dryer if he can't manage to dry completely with a partially damp towel.
If he continues to honk, after doing all this, you need to get him checked out.
You can use antibacterial hand gel on his underarms every night for a week and see if it changes his pit bacteria balance- this might kill off the smelly ones. Also use coal tar soap for a week and see if it makes a difference.
Fwiw, there has been recent research done on sweat and smelly sweat in particular and the findings show that a diet full of tomatoes of all things, make sweat really smell. There's a chemical in tomatoes, which reeks when broken down and eaten by skin bacteria.
Maybe try cutting tomatoes, and ketchup and beans in tomato sauce out of his diet completely as well.