Since I am not yet a parent, I am sure that I have no idea what taking out a child in public entails. Nevertheless, I feel compelled to say that working in a retail environment has often shown me what NOT to do as a parent. Here is exhibit A : The Child Leash.
First of all, your child is not a pet and should not be put on a leash like you were taking him for a walk.
Secondly, if you feel like you have no alternative than putting your child on a leash, then maybe you should not be yet venturing out in public with said child.
Lastly, it simply looks awful.
Also, I don't think that screaming at the top of your lungs at your child is an effective form of communication. I may be wrong here, but I think all that that accomplishes is making you look like a total mental case.