[vipermath]

We found a very cheap "grippy" material to use inside our pincers on our robot last year and it really works without causing any damage. I'm not sure how it will work on the track ball.

There is a rubbery type matt used under rugs to keep them from sliding or under table cloths to keep them from sliding off. It comes in rolls. Some people use them to line tool boxes. It only costs a couple of bucks at Walmart. Try it out. You will find it in the table linens section.