Training

Sure, off lead training is possible.  Leash manners are a better alternative.  Exercise in a safe area off lead is great.  There have been plenty of well trained dogs who died because they were off lead and unexpectedly bolted for whatever reason.  Not worth the risk in my opinion.
 
As to how, start taking organized obedience classes or get in touch with a private trainer (much more expensive) to get lessons.

First thing is he needs a 100% recall before you let him loose.  Get a long line and practise his recall over and over, starting withlow distractions and working up....  Reserve a special reward for recall that he does not normally get at any other time - it will make him work harder for it.  This might be an exceptionally yummy food treat (like homemade liver cake, which is easy to make but STINKY!) or a super special toy... whatever motivates him.  What is his favourite thing?
 
Take care that you only ever say your recall word once each time - at first only as he is already nearly at your feet so that he can't get it wrong.  Don't call him if you think he may not respond and you can't enforce it - this will only teach him to ignore you.  Walk up and collect him or move quickly away and reward him for coming after you.  And the Golden Rule:  Never scold or punish for a poor recall.