Depends on the dogs. I rescued a 4 month old basenji (male) from some people who bought him from a backyard breeder. I already had a 5 yr old male (neutered) and a 3.5 yr old female (spayed). At first it was like a mommy, a daddy, and baby. Til the baby got a few month's older and tried to take on the 5 yr old male! Pup was neutered around 6-7 months or so. It was fine for awhile, until it wasn't fine. There were knock down drag out to the death fights! Which ever dog Jenna felt like was winning, she would join in to help. The 5 yr old male (Dannii) was her uncle. Adult son living at home then, and even with his help, we had a hard time breaking the fights up. A friend recommended basket muzzles for all 3 dogs, which I did; and boy did they truly help. Dannii eventually came down with Lymphoma, and I think Zak (pup) knew Dannii was sick, so the fights kind of stopped. Not the growling or snarking but the knock down fights did. About a year and half after Dannii crossed the bridge, and tri basenji came into our lives. His owners were transferred to Brazil for their work, and couldn't take him. Mr.T was around 2, Zak was 7, and Jenna was 10. They had all met at a dog park on a few occasions and got along great. We met T and owner's at the same dog park, and they brought all of T's vet records, and toys and such. We walked back to my car, I opened the door on passenger side, Mr.T jumped in and settled down on passenger seat.........he was ready to go home! 3 years ago, T and Zak had gotten into a bad fight (the first and only so far). Again son and I had a hard time breaking the fight up. Zak ripped up T's left ear to where I had to take him to the vets and he needed stitches. They have been fine since. Zak is now 15.5 and semi deaf, not alot of energy; Mr.T is 8 now. Jenna crossed the bridge a year and a half ago at 17 years. So, I only have two boys now. T is snarky with Zak at times. He doesn't like it when Zak gets too close to him for some reason, so he will growl. Not sure if Zak can hear him or not, but nothing else has happened as far as any fights breaking out. T will just get up and move........hence the growl. Like the other's have said, "it works, until it doesn't work". Always introduce dogs on neutral territory. Since Zak and Jenna had met T at a dog park on a couple of occasions, which is why I think they thought it was ok for him to be in the car and their home.