I have had cats all my life and we always let them go outside. They were very pampered, don't get me wrong, but where I grew up we just always let them go out, and I still do. They always know how to get home.
I had 2 cats who lived this way (in various environments) and they lived to be 18 - 20 years old. We only had one scare where one of them (Bob) didn't come back for two weeks. But then he re-appeared (thankfully). One was a fighter (Bob) and he would escape no matter what we tried to do to keep him in. He was an incredible cat - he just could not be held back - fences meant nothing to him but a challenge.
We have 2 cats now and they are just too lazy to go far, so they go into the back yard (fenced in) and hang there. Now that they are getting older I find they go outside less. But we have a new kitten, and I don't think I'll let her outside unless we're with her, if at all. She hasn't tried to escape yet, but I think it's coming.
Anyway keep Chowder's shots up to date. I'm not sure there is much you can do if Chowder wants his freedom. I heard someone say once that a dog will risk his neck by sticking his head out the car window just to experience the sheer joy of the ride. Maybe Chowder thinks the joy he finds outside is worth the risk.