If you aren't already, I would recommend contacting a therapist who deals with this sort of thing. I, also, have had a picking problem for over a decade now. However, instead of picking my visible skin, I have an "obsession" with picking the dry skin off of my scalp and also plucking (which is kind of like picking) hair from my body.
If you're not ready to seek help, I would try to wear clothing that covers visible skin. Perhaps a pair of pants and a long-sleeved top. Also, you could wear gloves, which would prevent you from being able to dig into your skin. If you do this for long enough, the urge to pick may subside.