We had a lot of problems with my son running. We were able to get handicap tags for our car to help with this (at least in the parking lot). Maybe your states' DMV allows this too.

I used a child harness with my son for the same reasons. Any type of open space (hallways, malls, etc) compelled him to run to the other end. I lived in fear that he would run out into a parking lot and get hit. The harness was really backup for training him to hold my hand. I would hold his hand and the leash would be slack between us. If he should dart, the harness would stop him. I was self conscious that it would look like I was walking my kid the same way I would a dog. Along with therapy, I probably used the harness for about a year.

Do whatever it takes and do not worry about what people think. Keep your son safe.

I used a child leash. They sell some at Wal-Mart that have cute little animals and you hold the tail part. It was a good early solution for my family.

Yes, I frequently use a leash on my 4 year old, it does help. Check before you buy one that the child cannot remove it. I hqd a Velcro one and he figured it out pretty quick..