Well the only problem I ever had was when we introduced a puppy to our older dog who had arthritis. As long as we kept the puppy from bothering the older dog too much though, they were fine.
We always introduce our dogs slowly on neutral ground (on a leash) like at a park or somewhere similar before letting them meet at home.
My current dog was with us when we got a new pup for her. We made sure they we ok first. She loves him now and they sleep and play and hang together all day. Dog 1 is female age 3, dog 2 male 10 weeks.
I've been reading Cesar Millan books about dogs getting on. They should be fine if you do the right things. Make sure they understand YOU are the pack leader. His book "Be the pack Leader" opens with a story about 2 dogs that didn't like each other. Cesar sorted them out quickly and now they are fine.
I have a 3 year old male chihuahua named Hercules. We recently got another male chihuahua, 6 months old, named Zeus. It was rough at first. Put the new dog into a cage and let the current dog smell and investigate for at least an hour. I did that and it helped immensly. I let them play together too but I supervised so things didn't go bad. When the puppy started getting too hyper I stopped the playing because he would nip the legs of my first dog. Supervise them whenever there together so they don't fight.
my grandma has 4 and they were always fine
we have a dog named gizzy and she is 12 and we got a new dog named linny in may or june but he is in between hyper and playful
my grandma has 4 and they were always fine
we have a dog named gizzy and she is 12 and we got a new dog named linny in may or june but he is in between hyper and playful