At the farmers market, we are sometimes asked: "How long should I cook this roast?" The answer to this depends on two key factors: the size of the roast (ours are typically between 2 and 4 pounds) and whether or not it is thawed or frozen. As one would expect, the larger the piece of meat, the longer it will need to cook; and likewise, a frozen roast will need more time than a thawed roast. With these considerations in mind, I find that somewhere between 6 and 7 hours on 'high' (with about 2" of water in my crock pot) yields a fork-tender roast--if the roast does not easily fork-apart after this length of time, I leave it in longer. From a flavor and stock-generating standpoint, if you are using a boneless roast (such as a rump or sirloin tip roast), I would suggest adding in a soup/stock/shank bone during the cooking process.