If you have the dog house he's always been chained to, he may avoid it to avoid the bad memory of being chained. Sounds like he's got free reign in the yard now that you have him. Maybe build him a new house. Include him in the build, build it in his presence. Have him walk/stand in it while its just studs and a floor, before you close it in. Just thinking out loud, but ya never know. They are smart animals.
