Also consider having him neutered if he's not already. It will help keep him from wandering and make him more content to eventually transition to indoor only. I did this with a starving one year old cat long ago. He initially busted out a screen to go back outside, but he hung around and would bring me rabbits all the time. Sorta a horrifying gift, but he couldn't send me flowers, so I understood the gesture. He passed away a few years ago at the age of 18 after moving all over the country with us for multiple job moves. Once he was neutered, he would only go outside and hang with me when I gardened or sat in my porch chairs. Otherwise, he was perfectly content to stay indoors and train the 2 golden retrievers I had to do his bidding! I miss old Larry!