I am the warden

Choo-Choo has absolutely become infatuated with the outdoors. He has now taken to bolting out the apartment each afternoon when I come home from work. And in an effort to be accommodating, I stand outside as he explores. However, after about half an hour, I'm ready to go in and relax. He on the other hand wants to keep going. As such, I would leave him out in the small front garden on his own, but as the days went by, he got bolder and bolder and started to stray. When this happened, I would panic and start calling his name. Luckily I've been able to find him after a few minutes but it’s at the point where I don't trust him to be out there by himself. So I bring him back in and the tantrum begins. He'll run to the top of the stairs and start howling. Yup, howling. Then he'll proceed to come back down and start scratching at the door. In an effort to appease, I've tried to put him on a lease to take him for a long walk. But he does not want to be on leach. I’ve also opened the downstairs windows so that he can perch up and look out. But I’ve had to put this to a stop as he’s now jumping down into the garden. So I'm starting to feel like his jailor. Perhaps if he wasn't declawed and we didn’t live so close to a main road I wouldn't be so protective. Either way, I'm not comfortable letting him out of his own. I’m afraid he’s going to get hurt or worse yet, lost. So I’m uncertain of what to do. He looks outside so longingly that I’m starting to feel like his jailor.