Are these two dogs neutered? If not, they will be spurred on naturally by testosterone to best the other. They will be competing for dominance in the household. You may also need to separate them at night so they have their own space, or make sure to given each one individual attention away from the other.
Introduce them on neutral ground. Walk them together and don't be tense and anticipating bad relationship with them. When you see one going after the other give them a correction and say no to them. Let them walk together on a walk this will get rid of the pent up energy and it will let them calm down and submissive.
Putting two male dogs together can be very difficult. They will fight to figure out who is going to be the leader or the "alpha" male. Have you figured out what sets of them not to get along? You could try to feed them in separate areas of the house. Usually the dogs will work it out amongst their selves.
You may never get them to get along, some animals just don't like each other. However, if they are not neutered, get them neutered. This will help calm them down. You can also just keep them separated.
One strategy is to keep them near eachother for prolonged periods of time but do not let them come into contact with one another. Often, time is the biggest requirement for getting two dogs to get along.