When my husband and I got married, we each had a dog. I had a 6 year old boxer and he had a 1 year old schnauzer. We introduced them on neutral territory and they have gotten along well ever since; 2 years now. It really helps if only one dog has an aggressive personality. In our house the schnauzer is the boss. All 20 lbs. of him! Boxers are not known as aggressive dogs (unless they're trained to be). They are usually a good breed to introduce to other dogs.