We have three rescues. The first one was about 1 when he jumped into my car. He came home to three other dogs who, over the next two years, slowly died. We thought he was lonely and needed a companion so we put out feelers. A "friend" was moving up north and we ended up with her beautiful border collie - a male with behavioral problems from sharing a backyard (and little attention) with a Rottweiler. Then I found a little terrier walking our streets alone after dark and brought him in while trying to find his owners. No response so voila! we have 3 dogs. The first guy, part German Shepherd (we think) and part terrier, gets along great with the little guy. They wrestle and groom each other while the BC looks on and barks playfully. The BC doesn't like it when my wife shows little guy too much attention, baring his teeth, drooling, snapping and snarling, channeling his inner Rottweiler. My friends think we should ship him off because he messes with the household vibe, but who else would love him? I do wish we had stuck with the male/female matchup like we had originally planned, but a third, especially a male, would probably have thrown the dynamic off anyway. My advice? Match breeds with your biggest dog.