You say he isn't good with strangers --- only strangers, or the family too? Personally I love a dog that wants to protect it's family. No matter what you do, you can't make him want to protect his family any less. He sees it as his duty. You say your mom is a fraid of a law suit --- you mean if he bites someone? If that is a risk, don't let him have access to the public. Hang up both a "warning; guard dog" sign, AND a "do not tresspass" sign. You'll need both if you don't want to be sued by someone claming to have been bitten.