A male dog often sees another male as competition, especially if they meet as adults. Whether you're looking to bring another male into your home or just want Rufus to get along at the dog park, some social etiquette is in order. Ideally, socializing male dogs should be a relaxed, step-by-step experience -- rushing through the process could result in a fight.
Neuter your dog if you haven't already. Intact male dogs are more likely to fight, just because all those hormones will get in the way. Bringing a second male home? Make sure he's neutered as well.
Keep the initial meeting under control. You need another person for that -- either a helper or the owner of the other dog -- so both doggies can be on a leash. Keep the dogs close enough that they can see and smell each other without being able to touch. This will prevent bites or quick snaps that can easily get out of control. If things look calm and there's a lot of tail wagging during the first few minutes, let them get closer together, without letting go of the leashes.
Observe their body language for a while. If both dogs appear relaxed, it might be OK to let go of the leashes and let them play together. If there's any raised fur, growling or tense body positioning, separate the dogs and give them some time to calm down. Once they relax, get them close to each other again.
Watch for signs of dominance, but don't intervene unless you think a fight is imminent. Any time you introduce two males, there's going to be some struggle for "Top Dog" status. The struggle could be light and involve just a few growls or a couple of barks. As soon as one of the dogs retreats, the other is likely to let it go. If you have two boys who will not back down, things can get ugly. In that case, it might take longer and require more "neutral" meetings before a civil social relationship can be established.