Rottweilers..... Mine are VERY smart,easy to train even at older ages,and don't bark alot except when something is going on.most loyal obedient pet you could ever own.only reason not used by police as used to be is they break bones and cause serious injury when they bite.strongest bite of any dog. they tend to over heat more than a Shepard because of short snout and dark coat but they are not as hyper and do not bark as much as most Shepard's.great dogs for truck rides or fishing boat trips. they don't tend to wonder off they only want to be beside you and protecting you and best of all if you get one that's not mean no one will take a chance they just look mean as hell.luckily mine will put a hurting on someone no doubt but are trust worthy and great around kids even small children