Train him to heel in a fenced area. If he pulls, stop and make him come back to your side. Reward good behavior  

 That’s a good looking strong dog! 

 Counterintuitive, but a longer leash. My last dog would always pull on a 6ft leash but at 15ft of lead he rarely pulled. 

 “Become a tree.” Start walking, and whenever the leash becomes tight, you simply stop, plant yourself like a tree, and don't say a word. Took a while but it worked for my pup years ago. 

 We've done this. She gets a treat when she's chill. Now she knows a short leash means business and a long leash means fun. 

 I will try this.