To the OP, a Lab is a good choice for the purpose you describe. Some Labs will greet and lick burglars to near death, and some Labs will take an arm off one. A friend's chocolate Lab, Zeke, was one of the latter. No way I could get in the truck or house unless Joe was there first. Otherwise I risked losing an arm, and the dog knew me.

I'm always impressed by recommendations for mixed breed dogs to obtain some combination of desired traits. These folks apparently know more about dog breeding than the thousands of serious dog breeders who collectively have spent the last few hundred years developing dog breeds to be the "best" at just about any number of jobs a dog can possibly do. Mixed breeds shouldn't exist outside of "accidents" IMO.

Sg