Re: trouble keeping hands up sometimes
It is in the way you punch. If you punch properly, where the hips and the shoulders drive the arm either into full extension, or propel them through the punch, then they will retract in the proper way. In other words, you won't drop your hands.
But if you are "throwing" your punches, punching just with your hands and arms, then you will drop your hands. Think of tying a rope around a rock and then throwing it at somebody.