Dobermans are definitely good guard dogs and they are very intelligent. My boyfriend has a doberman and his family has had dobermans for 25 or so years now and they absolutely love the breed. They're fast due to their sleek stature, they are strong, smart, obedient, but I wouldn't go far enough to say they are ferocious. Dobermans are not vicious, stubborn, dangerous, malicious, violent, or anything like that. As a matter of fact, they tend to be very friendly unless they feel threatened, but even then, they hesitate to bite. They usually issue a warning by barking/growling rather than just attacking as other breeds would (like the german shepherd for example). The doberman looks intimidating and has the ability to be aggressive, but they definitely make very intelligent, loving, and obedient family pets. If you're looking for a more ferocious breed or a breed more keen on attacking or biting, id suggest a german shepherd, rottweiler, pit bull, or akita. I hope this helps!
Lots of experience with dogs. I have a german shepherd, my boyfriend has a dobie.