training on a leash

Question
I have two 6 months english bulldogs and am trying to train them to walk on a leash.They will wear their dog collars,so i have put them on a leash and let them roam around with it for about two weeks.But they still wont walk on it.I mean, i have pull on them to even move.and i dont want to do that.What else can i do?

Answer
Try using a harness on them. 6 months is late for leash training to start so it's no wonder they're putting up a fuss.
A collar will cut of their air supply if you're trying to pull them, so they will automatically resist.  Harnesses should do the trick.