Believe it or not, chicken broth is the secret to making the moistest slow cooker roast beef. Although that may sound kind of strange, don't knock it until you've tried it.  The gravy is lighter and the pot roast will taste fantastic! Sure, vegetable and beef broths work well. But my experience has taught me that chicken broth is better tasting.  Chicken broth miraculously brings out all the flavors of this super moist slow cooker roast beef.