I used the thing that a crib with a top was for my own safety.
But then I thought ... you know, in pictures I looked like I must have weighed 150 pounds when I was a few months old. I really wasn't going anywhere. Plus ... I used to have a bar attached to my baby shoes. My mom told me that I was born with flat feet so she assumed that preventing me from walking would help.
I tried the same thing with my son. He was 17 at the time.