Taking Gizmo for a walk

So we got the great idea that since Gizmo always looks like he wants to go outside, we'd go get a harness and leash and take him outside. So we put the little harness on him and took him out into the backyard. He seemed okay in the back yard because I've taken him out there before (holding him.) We let him roll around and lay in the grass for a little bit. Then Miranda wanted to take him out to the front of the house, which seemed like it wouldn't be a big deal. It didn't work out so well was an abject failure. He positively freaked out and squirmed out of his harness and took off. We thought he was laying in some boxwoods between my house and my neighbors. After spending a few minutes looking for him in there, I found him in his backyard underneath an old beater truck he has. Luckily after coaxing him for a few seconds he came out from under the truck. Once we got him back inside, Syd and Cali started hissing at him. I guess because he smelled differently. Were going to take him out later tonight but I think we'll stick to the backyard.