For teaching the recall, I don't recommend using your cue word at all at first, but rather enticing your dog to come with a fun, squeeky, playful voice, a special toy that you toss behind you or some other way. And when he does come and is just about to you, use your cue word and praise/ treat like mad. The other way is to capture. That is, when he is coming to you on his own accord, praise and treat. Then when he shows signs of coming much more regularly, then add your cue word with the act of coming. The problem with using it first, before he is coming is that he may associate it with whatever he is doing at the time since he doesn't know what it means yet. You need to tie it directly with the behavior. Until that happens, don't use the cue to try to elicit the behavior. Cues don't drive behavior. Reinforcement does.
The other thing that happens often, which causes the recall to break down is that it starts to mean "punishment." Often people call their dogs from a fun time and the fun stops or nails are clipped, or the leash is snapped on and the dog is taken from having a wee of a time in the park. When your dog comes to you and you want to snap on the leash, turn him loose again. Don't end the fun in association with coming. Do that a few times, then when you must go, give him a high value treat and some more fun as you leave the park. (example) Go get him when you have to clip nails or bathe, but spend a few minutes of fun while he's on the leash before you do those unpleasant chores.
Be sure to only practice the off leash training in a fenced area. If you use a long line out of necessity, still try to entice him rather than force him to come. Hiding behind a tree or bush and making silly noises sometimes attracts dogs to come and find you. You can play hide and seek. And always make coming to you the most wonderful thing. Never ever associate even the most mild punishment with come. Some things are punishment to a dog that we don't think of, as the examples above.....leaving the park, coming inside after playing outside. Continue the fun after he comes.