Cook a beef rump roast in your slow cooker for the better part of the day and you're virtually guaranteed to come home to a moist, delicious meal. A slow cooker, such as a Crock Pot, traps the beef's natural moisture -- and any additional liquid you pour into the pot -- during the long cooking process, eliminating the possibility that the rump roast will dry out.
Spread the onion slices and chopped carrots across the bottom of the slow cooker.
Trim any large pieces of fat off the rump roast. You want some fat to remain to help keep the meat moist.
Make approximately 12 small, shallow slits in the roast with a sharp knife. Space the slits evenly across the roast. Insert a few pieces of garlic into each slit.
Sprinkle the rump roast with 1 teaspoon salt and 1 teaspoon pepper. Place the roast across the onions and carrots in the slow cooker.
Pour the Worcestershire sauce and beef broth over the roast.
Cover the slow cooker. Cook on high for 4 to 5 hours, or on low for 6 to 8 hours. Insert an instant-read thermometer into the center of the roast. If the temperature is not at least 145 degrees Fahrenheit, cook the roast for another 15 minutes on high, or 30 minutes on low, then check the temperature again.
Place the rump roast on a platter. Cover it with aluminum foil and let it rest for 15 minutes before slicing.