Although it is very rare to end up with a rook against a knight with no pawns, it is still important to know that a knight can draw with correct play. The important point is to keep the defending king and knight in close proximity of each other, never to be widely separated. The attacking side's problem is that his king needs to approach in order to have a chance at mate, but the knight can chase him off with checks. This technique is discussed extensively in Karsten Mueller's DVDs on the endgame. If you have Fritz9, you can test yourself against it by using Fritz9's Endgame Training feature. Try it for yourself! In this example, try working with the Move List.