Duncan at 5 months is getting much better with biting and nipping, however, he's recently started lunging and biting at my wife more often. It's very strange, he won't do it to me, or other males that come by, but he does it to my wife all the time (chases her, jumps up and bites her, bites her feet, hands, etc.) and is relentless. He won't let up on her but virtually ignores me if she's in the room. It's not every single day, but frequently enough.

She grabs his snout, tries talking in a deeper voice, tries to pin him down to say "no biting" but nothing is working.

Is this an aggression issue? He's not growling, barking or baring his teeth but he's getting to be a big dog and don't want any serious issues. He's scheduled to be neutered in a month, so I don't know if this has anything to do with it.

Any advice or help will be appreciated. He also displayed similar behavior to my wife's friend the other day, but was totally fine with her friend's husband.

It is possible you and other men have been more quick an more persistent about correcting him for biting. Your wife might try the technique of yelling ''Ouch!'' and turning away. It is what a litter mate would do if bitten too hard. Training instinctive behaviors out of a dog takes correction after correction and absolute consistency. Something bad has to happen every time he bites anybody.