We have two miniture dachshunds but the male cannot be taken for a walk without showing aggression to any other dog we pass. He also shows this same aggression to visitors. Any suggestions?

One thing that would help is strong leadership on your part. If you are in charge, then he doesn't have to defend the pack. The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at Raising Your Dog with the Monks of New Skete For more on being top dog, see Establishing and Keeping Alpha Position, Letting your dog know you are the boss

Be careful how you react too. Control your emotions. Let him stress you, and he will think it is the other people or dogs, confirming his behavior.

Thank you. He is very submissive to myself and husband but still continues this behaviour when we take him for a walk and when someone tries to pat him etc. Yes, I will do some reading and keep trying - obedience class helped a bit, he did all the commands but wouldn't let any of the other dogs in the group approach him or get too close without going ballistic.

He may be submissive with you & your husband, but there is something that is missing somehow or else he wouldn't be reacting this way. He does appear to feel the need to protect or keep others away. It could be that he is the result of poor breeding practices, but it is hard to say. In any event, it is important that you both firmly establish yourselves as the Alpha leaders of the pack, as labman has advised. Please read through his links carefully, especially "Establishing & Keeping Alpha Position..."

Don't allow your little boy to be elevated above you in any way. If you allow him on the bed or couch, do not allow him to claim his spot first. Direct him to remove himself ("off" or "get down"-whatever words you use) tell him to "sit" or "lie down", and "stay." Get yourselves settled and then you can invite him up. If you are consistent, what will happen is that if he is lying down in one of your spots, he should jump down or move and look uncomfortable, when he sees you coming, he will stand and wait for you to get comfortable before he makes himself comfortable. Make sure he does not claim a spot on the bed above your chest and shoulders. The highest up he should be is your lower chest level. Do not allow him to lay across or on top of you. That is a position of dominance and you will be reinforcing his leadership.

Never break eye contact with him. If he is staring or looking at you, stare back. Force him to break eye contact first. Do not allow him to just jump into your lap without being invited. Do not allow him to be the one to initiate play. That is the leaders job.

In addition to following our advice, when you have visitors come to the home, the minute he displays this aggression, you need to use your body to block whoever he is focusing on, and get him focused onto you. Direct him to the "lie down" and "stay" positions. The minute he tries to move or makes any noise, give him a very firm "NO" and stand over him. He needs to know that you are in complete control of every situation so that he can relax and be the follower, not the protector. Block his view of whatever it is that is making him respond negatively and force him to focus on you, his leader. "Sit" or "down" commands, then "Stay" command. Do not allow him to move until he relaxes and is completely calm down. Then you can give him your signal for release. Tell him "good boy", pet him or just be very happy and excited when you tell him he is a good boy for listening to you. At the beginning of this retraining, if he is food motivated, you can give him a very small treat once in a while as reinforcement.

You can use the same technique when you are out walking or a different one, which I will outline. Whichever one works best for you and your dog. Whenever you are walking he should always be in a heel position no matter where you are, not pulling on the leash or ahead of you. If you use the technique outlined above, once he calms down, again, "good boy" in a happy, relaxed, excited voice, and continue your walking/heel. The other technique is to just to keep walking, give him the heel command, snap the leash gently to focus his attention onto you, keep your head and shoulders held high and confident, your body positioned so that he is forced to move along with you and he can't get a good look at the other dog, leash should have very little slack and you should have a good grip on it so that you can correct him, and KEEP WALKING. Force him to focus on you and follow you. He should not be easily distracted by anything around you. When a dog recognizes who is leader of the pack, they look to their leader for direction on what is expected of them.

Great follow up and expansion of my answer.