How do I fix this cat?

I'm definitely an outdoor cat person...heck...at this stage I'm an outdoor animal person period. We also have a St Bernard too. Average age of a St Bernard is like 6-10 years. Ours is 9 and I've since began marking the days off on a calendar. Already have his hole dug. Our outdoor cat is cool....he's like any other tool you have around the house. He does a job and does it well. Not a single mouse left around our house. He stays in the garage at night and then we open the back door in the morning so he can come and go unless it's really cold out.

I don't know if any of you have seen a St Bernard eat but he only ends up with about 40% of what he eats in his belly. The rest is all over the floor and anything within a 5' radius of the bowl. We feed him in the garage because of that. When he eats the outdoor cat eats dog food right along side him and then eats his food we keep up on a freezer. Not long ago the cat got a hairball and puked it up in the driveway....it had dog food, cat food, and pieces of mouse in it. ?