Personally, if the dog's off leash, I wouldn't even use the word, "come" unless you're positive the dog is going to or unless he's like two feet from you, obviously coming. At that point, say, "come" and then reward like crazy. Instead, if he's off leash, don't tell him to come. Just run the other way, make very fun, silly noises and see if he'll come. Squat down with your arms outstretched in a very happy way. See if you can entice him to come without using the word. Then when he does, use it. This way he won't get conditioned to hearing the word, but not come. If you have to go chasing after him when he ignores you "come" command, too much time may elapse and he'll lose the connection. It's best to have a leash or long line on him to help him obey your command or do the other way where you entice him to come without actually giving the command....that is, until he's just about to you.
I prefer motivating the dog to come, rather than pulling him in with the long line, if possible. This makes him decide to come and anytime the dog chooses the "right thing to do" (lol) he learns better, gets smarter, than giving him no choice by forcing him to come. Try seeing if you can make coming to you the best thing in the world...special treats, lots of praise and don't say the word, "come" unless you're positive he's going to. It will snowball the more times he is successful in getting a payoff. He'll get better and better. This is how I taught my Dobe and he has a very very reliable recall, even when in mid chase of other furry creatures.