Kids on a Leash - What's Next?

I don’t understand the idea of putting your kid on a leash. If you’re going to put a leash on your kid, why not forget the diaper and just have them go potty in the front yard? Okay, going potty in the front yard might be a extreme, but they actually sell leashes for kids, and people actually use them! No, I’m not making this up. I saw people using these at the zoo the other day.
I appreciate the fact that you don’t want to lose your kid. But, there has to be a better way to watch your child. Right?