I prefer to use a regular dog harness and loop a flat leash around the stomach. I've yet to meet a dog who has had to have the leash tighten around the stomach more than once before they walk nicely. It may seem mean because they normally overreact when they first get the sensation of tightening around the midsection, but I believe it is less harmful than the neck or head. It also allows them the freedom to sniff around a bit since their head isn't involved.

I do not consider controlled walks at heel to be enriching exercise, be it a walk around the block or 5 miles at heel. That kind of walk does nothing for the dog's brain and can hardly be expected as a release for their pent-up boredom. If you have a dog you simply can't walk on a loose lead then you need to find a way to get that dog some off-leash exercise in a safe area.