I used a baby safety harness for my son, also a great escapee.
It was also used when he was in his pram and later, when walking beside me.
He was still a Mayhem Child though because even in the harness (which slid up and down the vertical bars of the cot) he could stand up and shake-rock the cot so vigorously, that it moved across the room.
to his great delight.
I have seen so many toddlers running away from parents who seem to have the idea that the harnesses which kept my generation's little ones safe, are somehow wrong.
Just 2 days ago whilst waiting outside the pool for my driver, I saw a wee boy of about 2 run right out into the very busy carpark. But for the quick reflexes of the young driver, that toddler would have been hit.
His mother, several steps behind didn't seem too bothered, so maybe the child does this all the time. He certainly had no road sense whatsoever, didn't even hesitate at the kerb.