I want to second what Juno added.  Our Juneau, a 5.5 month old female, has followed a progression path like many of those already described.  Grew very strong, very quickly, and with her pulling made walking very challenging, despite many different typical tactics attempted: start/stop, change direction etc.  The choke chain worked for a bit, but her tolerance (and ever strengthening neck!) made that less and less effective.  We too have recently discovered that proper collar placement and leash holding technique is a night and day different.  Once the choke/slip collar is on correctly (ie "active" length going over the neck) we position the collar so that it is directly behind the ears, basically as high up the neck as it will stay.  We also keep a very short leash (not tight, just very little slack), at least to begin with, which allows for very timely correction, and the ability to keep her nose from breaking the plane of the walker's knee.  Furthermore, it prevents the ever curious nose from getting too close to the ground and creating more distraction than she can handle.  The net result is that we can control Juneau (who is already 35 pounds) with just a couple of fingers - and most importantly she has taken a renewed interest in following, not leading on the leash.  We too figured this out from watching Cesar.  It is still in its early days for us, but thought I would share with others.  For what it is worth, you do have to keep lifting the collar up in order to maintain its position - I think using one of the lighter nylon-type leashes that Cesar uses would help remedy this.

Depending on the dog almost any collar positioned right behind their ears will work in the same way.  That area is the most sensitive area and it works like a rudder to steer the dog. 

For those that see a behavior difference when they put the ecollar on, you have a collar wise dog.  Meaning they know where the correction comes from.  The way to prevent a collar wise dog is to put the ecollar on them when you get up in the morning and let them wear when they go out or whatever.  You have to do this several weeks before you ever use the collar.  That way the collar is just part of the routine of going out, for a walk, whatever.  When you do use the collar they do not associate the correction with the collar because they have already been wearing it along time. 

I got to test my boy this weekend on his recall without the ecollar on as the AKC does not allow ecollars in a hunt test.  Ringo is testing for his Junior Hunter. He found and pointed 5 birds and qualified.  Since we were the last brace yesterday he also found a couple of wounded quail and ran them down.  I was worried that he wouldn't bring them to me as we have not worked on retrieving a real bird yet, but when he scooped up the bird I called here and he turned and brought it right back to me and dropped it at my feet when I told him drop it.  The judge laughed and said the retrieve wasn't needed for Juniors. Most of the other Junior dogs that caught birds played with them and wouldn't go back to their handlers (all of played the chase game and so they lost valuable hunting time as these tests are timed).  Anyway, if you get that reliable recall without making the dog collar wise there are lots of useful applications which is why I mentioned it in the first place.

Good luck on Juno's successful walking on leash.