I think it's important to get a very good recall first by keeping the dog on a long line and training it using motivation/reward methods. If you give a command to come and can't do anything about it and the dog doesn't come, you're in trouble right there. Never give a command you can't enforce. Make it extremely worth it to the dog to come every time. All dogs need to eat. Food is a good motivator, especially when it's something very extra yummy on an empty tummy. LOL.
When your dog has a very solid recall, first in low distraction areas, then gradually increasing the distraction level until he's coming in the midst of a lot of different distractions (safe)....then let him off leash in a safe place....never where he can get hit by a car or where other dogs are. Dogs can run a long distance in a heartbeat. No dog is 100% reliable, even the very best trained ones. They have drives, instincts and some situation that could come up, that sometimes override their training. Good recall training doesn't happen over night. It takes lots and lots and lots (did I say lots?) of practice along with the dog's maturity.
Don't forget to praise your pup everytime he comes around you, even if you didn't call him. Make games and fun when teaching him to come....run the other way, entice him, play hide and seek and give him a treat when he finds you. Never punish him for something else when he comes and don't stop all the fun right after he comes. If you're outside and need to go in, if he comes, go inside and continue with another game for a little while. That way he doesn't learn to avoid coming to you because the fun is over. If you call him to come to put the leash on him, walk around for a few steps and release him again. Make sure to end training sessions on a good note and show him that coming to you is the best thing in the whole universe and that it doesn't mean it's the end of a fun time.
If I ONLY walked my Doberman on a leash, in order for him to get enough exercise, I'd have to walk from north Idaho clear to Miami. Thankfully, I live in a wilderness area where there are loads of safe places for us to hike and for him to run, including my own property. But if you don't have this and a park works for you, that's an idea, although I'm not a big fan of dog parks.
Hope these tips help.