I have a 6 yr old Rott, when he was in his cute puppy stage he started showing aggresion like if we took his toys etc. didnt really want to listen to us, well we had a trainer who lived across the street from us and she let us know we could NOT tolerate that behavior no matter how lil or cute he was, so we didnt, we had to put our foot down , and raise our voices with him let him know we didnt tolerate it, mostly my boyfriend did the training cuz i couldnt do it, but... he growled at us once when he was 6 months old i think, and 6 years later, never ever again, he is soo gentle and loving truly a great dog, but he still has his aggresive nature in him, with strangers. You should get a profesional trainer if u cannot do it yourself, Rottweilers are the kind of dog that need firm training, they need to know who has the upper hand, we used all the same training with our Presa Canario who is larger than him and the breed has a worse "reputation" then the Rott, and she is as sweet as can be.