Nunn Bush must have changed their manufacturer because the last 3 pairs I've had only lasted a few months each.  I found these models 12 years ago when I started in corporate IT and would wear them for at least a year before having to get another pair.  Recently, I've gone through 3 pairs and they've all just disintegrated over the course of just 2 months, one pair the sole covers came detached after a few weeks.  Sorry but they just aren't what they used to be.  I've moved on to Rockport and they so far are holding up nicely.