Bryan,
Get an English Mastiff. You won't need to fence cause the dog will stay wherever you are.
They don't wander like other breeds. At least mine never did/do.
If you are inside they'll go out to do their business and come right back in. They like to keeep their master within eyesight. If you get up and go into another room where they can't see you they will get up and move to a spot where they can see you.
http://www.dogbreedinfo.com/mastiff.htm
Don't let the size scare you, they eat about the same as a Lab.
NO ONE will f' with your house or stuff with one of these around.
They are really sweet animals. My 20lb. Mini Schnauzer had 10x's the attitude than my 200 lb. Mastiff.