I can only speak for what I saw done first-hand. Some guys used their own shanks/shivs/whatever you want to call it, basically any old piece of metal. This was obviously done in their cells on their own. Much more frequently [and out in the open] though was guys using the plastic butter "knives" that came in the dinner trays (think KFC, individually wrapped sets of 1 plastic spork, 1 wetnap, and 1 plastic butter knife with a kinda serrated edge - though still dull as all hell). For doing the divots we used the end-tip of the long piece on the cap of a typical old-school style Bic pen - this worked extremely well and quick.