any suggestions on how to stop a saint bernard puppy from being aggressive towards others dogs?

Try not pulling back on him, dogs see this as a sign to be afraid or react to why your pulling on them. Called Leash aggression. Instead, let him go twards the dog smell the other dog, then praise him for good behaivor only. My saint bernard had the same problems. This is working for me.

You need to become the leader or dominant of your dog, the dog is trying to become the pack leader, because she feels like no one else in her pack is the pack leader. Try not to let the dog lead you on walks, make her walk besides or behind you, also never let the dog enter a place first as this will cause the dog know, that you are the submissive and she's the dominant. Also, when you see her acting aggressive towards another dog, try making a 'sh' noise to stop her from barking and growling, if she doesn't, give her a gentle (very light) touch to the neck with two fingers. You need to nip this problem in the butt and do NOT listen to others, who think its cute, its not and its dangerous, this problem will grow and become an even dangerous problem then before.

Well, obedience school usually does the trick, but evidently your big boy is feeling his stuff! If you aren't planning to show him, get him neutered. this is a good age. If you aren't going to neuter him, then the head harness called the Gentle Leader will do the trick. You will have total control over him (and his mouth)as he gets bigger, and bigger, and bigger. The Gentle Leader also has a detailed instruction booklet showing how to handle aggreession, gently and safely. You may one day go back to the regular collar. All pet supplies have the head harness, and you can get it pretty cheaply on ebay...Best of luck to you and yours, and thank you for being so reponsible.

Obediance school and talking to a dog trainer. Your dogs needs to be socialized...

Petsmarts dog trainers will be a good source to go to for more advice.