It's very important for a boxer to have an owner who is dominant. Let it know that you, the owner, are the leader of the pack to help it get along with and like being around other dogs. Boxers are energetic and athletic and can be very protective of their owners. This means that a boxer that doesn't like other dogs needs to be watched closely and the situation needs to be remedied as soon as possible. Boxers are intelligent and highly trainable, so teach them from an early age to get along well with other dogs.
Keeping your boxer in a happy and healthy state of mind, which will help it to get along with others, starts with exercise. Boxers need a lot of active exercise, and at least one long, brisk walk every day. Not only is the walk important for its exercise, you also must consistently use the walk as an opportunity to let the dog know that you're the master. Don't let it be in the alpha position. You walk the boxer; the boxer doesn't walk you. This means that it walks beside you, not in front of you, and it can't be the one who decides when it wants to stop and sniff and which direction it wants to walk in. Repeatedly show your boxer gently, but firmly, that you're the master.
How Boxers Think
Boxers are very protective. It's easy for them to see another dog as a threat to your safety, which will make them feel that they need to be protective. When you're around other dogs with your boxer, use a calm friendly voice and attempt body language that makes it feel that you're comfortable with the other dogs and see them as friendly.
Provide Brief Socialization Opportunities
As the pack leader, encourage your boxer to socialize appropriately with other dogs. It's best to introduce social opportunities when it's well fed, has had some exercise, and is least likely to be feeling anxious. Correct your boxer immediately and firmly if it jumps up on another dog or acts aggressive in any way. Keep social interactions brief at first, with the boxer on a leash, heeling to you.
It's easiest to teach a boxer to get along well with other dogs when it's between six months and three years old. After that, it will be stubborn about changing its behavior and may continue to act as if it doesn't like other dogs. Continue to patiently expose your boxer to social opportunities with other dogs and never lapse in showing it that you're the master. Remove the boxer immediately from any situation where it's showing aggression that you're having difficultly curbing.