Male 2.5 over protective boxers

Question
I have two 2.5 male desexed boxers and a 4 month old baby girl. On the
whole the2 boys are very well behaved and trained. When i was pregnant my
red boy was very protective of my pregnant belly and would stand over me or
next to me when ever possible. He would show no aggression towards my
husband or anyone else, however if my brindle boy came to close he would
growl and even attack. We would show him this was not acceptable and he
would be placed outside for his bad behavior.

The red Romulus boxer still now displays this behavior around my daughter, i
don't believe it is directed at her, but when ever Abacus the brindle dog is
close he will growl. It appears to be worse when she is crying or in the bath.
He also displays a habit of trying to get in between her and myself, i am
unsure if he is trying to protect her or me. If it is me i fear he may harm her. I
am unsure what to do and how to read his behavior. Please help i love all
three of my babies and want them to be the best of friends.

Answer
He thinks he is your protector and is attached to you.

He doesn't want to share you either.

He doesn't want the Brindle to be near you or your daughter, so you will need to teach him it's alright and to share.

Buy a loud, obnoxious sounding whistle and blow it each time he growls and is aggressive. Use verbal commands; easy to understand. The "no, bad" is good, and "it is all right, Romulus-- be good" .... those kinds of commands. Change your voice tone from stern to softer and upbeat when using the words accordingly.

Be consistent and continue the training until he appears calm.

He will soon associate the whistle sound and your verbal commands to his aggression and stop.

Treat him each time he stops to reinforce positive behavior.

Keep an eye on him during the training.