Hi Pat. Thanks for the reply. Duncan is neutered and Mya is spayed. It would appear that Duncan is thinking that I am his territory and he does not want anyone or anything else in his area. When the aggression occurs I scold Duncan and remove him from the area he was in when the aggression occured. I also scold Mya and remove her as well. I do not give them any attention until for awhile until I am ready to, as I am trying to establish my pack leader role. Any other advice would be much appreciated.
I’m a big fan of Cesar Millan, The Dog Whisperer. Do you get the National Geographic Channel? He rehabilitates dogs and trains people. If you can watch his show you will get lots of tips on how to regain your title of “Leader of the Pack”. However, in aggressive dogs it really is better to get professional help and he definitely recommends that.
I would recommend any or all of the following books. Dachshunds for Dummines, Cesar’s Way by Cesar Millan, he also has DVD's(book and DVD's available at Amazon.com or CostCo) Leader of the Pack and Have you Dog Love you for it by Patricia B. McConnell. Also The Other End of The Leash by Dr. Patricia McConnell and Patricia McConnell's "The Cautious Canine" can help you boost your dogs' confidence levels.
There definitely is no quick fix on this one, just lots of hard work and commitment. Here are a few tips. Exercise regularly. At least 2 walks a day 30-45 minimum (especially the male), this will get rid of a lot of pent up energy. When walking, they must always walk beside you or behind NEVER in front. The NILIF (nothing in life is free) is always a good idea. They must work for everything they get. Make them sit and wait for their meals, you go out the door first and then invite them out. No sleeping in the big bed. Do not let them in your lap unless you invite them. In Cesar's words, exercise, discipline and then affection, always do it in that order.
Regarding the aggression. Your pups aggression will not stop and likely it will worsen if not corrected soon. What steps have you taken to correct him? Have you had both of them in obedience training?
With an aggressive dog you really need help, possibly from a certified pet behaviorist. This is a tricky situation and you might inadverently make it worse. Please seek professional help as soon as possible.