I use a protective case attached to an armband when I run and bike. For sweat getting into the headphone switch, try wrapping a cotton ball, piece of sponge, or some other absorbent material around the headphone cord above the switch. Attach it with tape. Change it out each time you run.
Oh, and remember to go into Settings and turn off "shake to shuffle!"
Oh, and remember to go into Settings and turn off "shake to shuffle!"