I'm sorry, but this is my honest opinion, but if you are concerned for his safety from dogs, wolves, coyotes and bears, then keep him indoors where he will be safe. I know he is an outdoor cat, but with time and patience they can learn to adjust to indoor living. I have done it in the past, when I was taking care of an older stray cat. One day he showed up in his cat shelter with a broken jaw. That was it for him, it took time and patience but he learned to live indoors.
There is another option. Slowly introduce him to a harness and leash and then this way you can bring him outside under supervision without any worries. As they say, "Better safe than sorry."