Stir The Garlic, Horseradish, Hot Pepper Sauce, Thyme, Salt, Pepper, Cajun Seasoning, Olive Oil, And Malt Vinegar Together In A Bowl Until Thoroughly Blended. Pierce The Beef Roast All Over With A Meat Fork. Place The Roast In A Large, Resealable Plastic Bag. Spoon In The Marinade And Turn The Roast So It'S Well Coated. Refrigerate Overnight, Turning Occasionally If Desired. When Ready To Cook, Place The Roast In A Slow Cooker Along With Any Remaining Marinade. Do Not Add Water. Roast On Low For 8 To 10 Hours, Or Until Desired Doneness. For Medium-Rare, A Meat Thermometer Should Read 135 Degrees F (57 Degrees C). Remove From The Slow Cooker To A Serving Plate, And Allow To Rest 15 Minutes Before Slicing Across The Grain.