I actually selected a retractable leash for my dog that was fat, like a full leash (NOT invisible), and I usually use it either REALLY short (right next to my body) or about 3 feet locked. The only time my dog gets out farther than that is if we're walking, she stops, and I keep walking while she pees (this is a frequent occurrence, apparently it is her job to mark every X feet), at which point she might get to about 6 feet.

A well exercised and well mannered dog won't wander regardless of leash, but it's usually not the dog's problem, it's the owner's. Don't train your dog? Don't walk them regularly? Don't give a crap? They aren't the ones that suffer. I've heard tales from the trail where people have been attacked by dogs at the end of the retractable leash while their owners don't pay attention (or worse, dogs off-leash). The only time we run off-leash is in winter when nobody else is using the trail, and only on segments of the trail where that's true. Once I invest in one of those leashes you can wear around your waist or whatever, that'll come to an end entirely.