I have a 2-year-old Rottweiler who is very loving to me. We got Brutus when he was only 4 weeks old. The people we got him from were not good people, and we felt as if we were doing him a favor — not to mention we fell in love with him right away.

He has had problems with both hips. He sometimes can hardly walk after play or a very short run. He has had knee surgery to replace an acl on his back left leg, and his front left leg pops out sometimes, and I have to put it back, which is extremely painful for him. But he does have good days, and although he limps sometimes, he doesn't appear to be in pain all the time. He can take off and run after the birds in the backyard when not having a bad day.

Brutus isn't aggressive with other dogs except for my daughter's Akita when she visits and if another dog shows him aggression. But he has become very sketchy and unpredictable with new people who come over. He tries to smell them by stretching out his neck and will give a low growl and sometimes urinate out of nervousness. In the most recent situation, he urinated a lot and was so nervous for the first five minutes, but then he was in love with the guest after that.

My wife took him to the mailboxes three days ago unleashed. I came outside when they were about four houses down, and he started trotting back to me. A woman walking her baby in a stroller was on the other side of the street. While he was crossing, he looked over at her and didn't slow down, but he let out a low quite growl and gave her a good long stare. After that, I decided that he will always have to be leashed. When I took him to the park, a kid about 13 years old and his mom walked by. The kid made eye contact with him, and Brutus went off in a big way. I tugged on his leash and told him down (which he did immediately), but there was no reason for it at all.

He is trained pretty well and will obey any command I give him without an issue. He has never been hit by anyone. I disciplined him once harshly for growling at my oldest son (18), who walked by him while he was eating a leftover ham in the backyard. I immediately grabbed him by the skin on his neck and the skin on his hide and tossed him to the ground. He submitted to me immediately, and I took the ham and threw it away. This is the ONLY time this dog has been shown any aggression from anyone.

This is my third Rottweiler in 20 years. I have never had an issue until now. He is obedient, but I don't trust him. He is almost impossible to stop when the pool guy or the gardeners come. Once he hears the gate open and shut, he flies out the dog door like he is on a mission to kill. I can stop him if he hears me, and he will go back inside, but it is a scary situation. We now make sure to put the divider in the dog door on those days, but Brutus is totally vicious at the sliding glass door the entire time they are here. On those occasions that he has made it to them, he has never bitten anyone, but it seriously looks like he is going to. I'd be grateful for any advice.

Something's gone wrong with the training, or something's gone wrong with the dog. Either way, Brutus certainly can't go to the park and probably shouldn't leave the yard until he's been evaluated by a professional dog trainer who specializes in aggression.

The fact that Brutus is in some degree of pain much of the time should not be overlooked. Brutus is painful and fearful, and fear- and pain-based aggression is unpredictable. Your best bet is going to be a combination of professional training that does not exacerbate his fearfulness or stoke his pain and careful management of his environment.

Brutus' world will need to be much smaller. Close the doggie door when the pool guy comes, yes — but also secure Brutus in a quiet room away from any windows that could afford him a view of the pool area. No parks, no off-leash strolls, no roaming the yard when people he doesn't know are in it, and no meeting new people, especially little people, until you feel confident in his training and his behavior. Until then, Brutus will have to live on your love alone, and he will be just fine with that.

Woof!

Dog trainer Matthew "Uncle Matty" Margolis is co-author of 18 books about dogs, a behaviorist, a popular radio and television guest, and host of the PBS series "WOOF! It's a Dog's Life!" Read all of Uncle Matty's columns at www.creators.com, and visit him at www.unclematty.com. Send your questions to [email protected] or by mail to Uncle Matty at P.O. Box 3300, Diamond Springs, CA 95619.

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