How can i prevent my dog from fighting?

I would use a dog crate to prevent them from fighting when you are not around. or make sure that they are separated eitherwise they will end up fighting.

Are they two females? Try to separate them during feeding time. They are fighting to show who is superior over whom.

Introduce them on totally neutral ground and on loose leads. Use a vacant lot, parking lot or at least get a few blocks away from your house and away from where you normally walk your dog. Don't even have your car nearby. The more neutral the area, the less likely they are to fight. Wait until they check each other out and actively interact playfully, not just passively tolerate each other. Encourage running and playing, but don't think they're buddies just because they aren't fighting. Try taking them on long walks or runs before putting them together. When dogs walk together it is a pack activity and can start them bonding as pack members. If they are all tired they will be less likely to fight. And start off slowly, exercise them and then have group time for about ten minutes the first time and work your way up. But you have to be committed to doing this everyday. Make sure you treat them all the same so they are not fighting for a higher position in the house, if they all know where they stand then they won't need to prove themselves. hope this helps :)

Are they both males or both females? Spayed/neutered? What breeds? How old are they? There's a lot of information needed here to give any kind of advice, but if they are fighting then you do have to keep them separated and consult a professional dog behaviourist specialized in aggression.

well i have 2 dogs 2.at what age did u intoduce them to each other?coz if u have introduced them at ages like 2 yrs or 1 yr thats the time they are highly active and get ready for mating.so the frustration of no mate makes them attack each other.get them a mate(m or f)acc to yr dogs gender