Safety issues is often used to justify punishment, specifically spanking.  The most common scenario is "I only spank when it's serious, like when my child runs into the road.

The safety defense of spanking is a red herring.  You can't punish children enough to keep them safe.  If you have a child young enough where running out into the road, outlets, scissors, knives and stairs are a safety issue; the only reasonable prevention is supervision.  You can't repeatedly spank a 2 year old, set them in the driveway and walk away.  You can't make a small child responsible for their own safety. 

It doesn't even help to 'teach them how serious this is".  If they are of running age, they are also of an age where they will not understand the magnitude of danger involved.  They won't connect "danger" with the punishment.  If spanking works/ed with your child for safety, it's because your child had that kind of personality.  A runner will require supervision, regardless of how many times you have hurt them in the past.

Here's a Better Idea

If you know you have a runner, you'll need to be proactive.

Talk to him in advance about the expected behavior. Have him tell *you* what's acceptable (staying near mom or other adult). Talk to him about the consequences of his actions. Talk to him about safety, but also about how your going out will be limited unless he can agree to be safe.

Use games.....come up with a song (or sing a hymn) on the way into stores. Guess together how many steps it will take to reach the store and count together. See how many blue cars you see on the way. Take big steps. Take little steps. Give him something to hold or carry to help you.

Use positive terms, telling him what he *can* do rather than what he can't. "Stay with me, holding onto my hand" rather than "don't run away".

Keep him engaged in conversation and activity.

If he does run again, do something related but dramatic such as take him home immediately. Explain you had to go home because he was "not being out safetly". Let your words and the action be the discipline, don't add another consequence or shame to it.