K.E.
My 22 month old is also a runner - and no amount of verbal calling is enough to get him to come back! He also seems to have the slipperiest hands on the planet, and can get out of even my strong husband's grip!
Out of desperation, we finally broke down and bought the monkey backpack with the leash for a tail. ($15-20 at Target) He loves it! Now when we go for walks, he holds his arms out for the monkey to go on, and responds great to being told to wait.
I was against the leash, partly because of the whole "my son is not a dog" thing, and also out of hesitation to the way others might react. So far, I've received nothing but positive feedback, people saying how cute he is, how well behaved, and even older women wishing they had had the backpack when their kids were young! Best of all, I'm no longer worried about him getting away or being snatched up!
To those who are against any sort of "leash" - I would respond with "Well, if I had to choose between putting him on a leash so he doesn't get away from me, or something beyond terrible happening to him when he does get away from me without one, I think the more humane choice is to stick him on a leash."