Heya all !

I recently bought a house in a really wild area, Im very interested in birdwatching and wildlife photography so this is a perfect place for me. Unfortunately the owners cant take their cat with them and I agreed to take care of him when i move for now. I want to make my yard as friendly to local wildlife as possible so letting him out is out of the question. He is fully grown, Im not sure how old and has lived his entire life outside, Im a bit worried its not even possible to convert him, I don’t want to take him to a shelter but if its not possible to keep him indoors without destroying the house I will not be able to keep him. Im a dog person but we have always had cats so i know all the care needs and an acess to a really good vet who is amazing with cats, but this is something new to me, all our cats are indoor cats from the moment we get them. Im thinking, would training him to be leashed help at all, hes fully grown so i also am not sure if it would work ? Im reading up on the issue on different sites as well but if you know any tips id really appreciate it if you shared !