Ollie pulls with excitement when we first go out until he settles down. When I was recovering from a frozen shoulder his pulling kept wrenching my muscles. I bought a Canny Collar direct from the makers website. I don't like to see dogs with a loop of lead around their muzzle but it was either this or Ollie didn't go out at all. I use the Canny collar as his everyday collar now and only very occasionally do I need to put the loop part around his nose. It is quick and easy to clip together for when he is off lead.
You could try some tasty tempting treats to encourage your son's dog to stay close. Dogs tend to like cooked liver and if you fancy making it how about cooking liver cake. Lots of wizzed up liver, garlic and flour and baked in the oven until dried out. Yummy
Otherwise chicken or sausage would do.
Do you have an enclosed dog park close to you where live?
As he is a Lab how about trying to use his natural instincts as a retriever. I was thinking about using a training line to start with (probably a long length of washing line would do) throwing a soft toy and calling him back, treating him and then gradually extending the distance you throw.
Labs are working dogs and love to carry things. Stick a toy in his mouth and hopefully while he is carrying it he will gradually run out of breath and slow down his walking pace.
Good luck.