We also had a bad experience introducing a new, younger female Boxer to our older male Boxer. They were fine for a couple weeks but then the newcomer attacked our older Boxer several times seemingly out of nowhere. It left him with a large hematoma on his ear and he had to get staples for a deep wound on his shoulder. We had to rehoming her.Unfortunately, my experience did not go well with 2 half brothers in the house. We got our first Boxer boy from a breeder in 2020. Two years later we had an opportunity to take in his half brother which was about 1 year younger. The adopted boy went from quiet and playful with our 2 year old Boxer boy and once comfortable in our home, he became very aggressive towards our boy to the point he attacking our sweet boy. We ended up taking him back to the breeder. I am hoping this was just a one of situation because I see so many social media posts of people with 2+ boxers in the same household of mixed sexes. This is our third Boxer. We had 2 females before and are totally in love with their affectionate and silly personalities!