I'm new hear been lurking a while and would never give grow advice to you pros. However I will give the best guard dog advice you will see in these posts. Pits, shepherds, and what not are ok, but the shepherd has to be trained really well and pits like fucking up other dogs most of the time not people. Ive walked into a million houses with pits that didn't know me and they licked me to death.
However the Fila Brasileiro is the most protective, dog and absolutely hates anyone other than the family he lives with, he wont let your mother or best friend who comes over everyday in with out killing them. Also these dogs are the most loyal family pet and will never bat an eye at your kids or baby's / toddlers. Get one and never look back. If you do get one, get them from a Brazilian breeder who breeds the old school CAFIB Lines. Super fucking hard dogs. Go to youtube videos and search CAFIB Fila temp test.