When Lucius hit puberty, he went from a cute puppy who got along with everyone to a dog who is not trustworthy around other males. I don't know that there's anything you can do to prevent it or stop it. Maybe there is... it was always treated by my breeder and breeder friends as something I was just going to have to learn to deal with -- and I have. Of course, I didn't have a male dog in the household to worry about.
Best of luck. Hopefully someone else will have some wisdom.
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