Deep pots as the well known 5 gallon plastic buckets. In Babianas the first (lower) pair of leaves always appear at ground level, with never any hint of a neck (say, a stem) visible. It is incredible how deep an established clump can travel to. A very well drained mix and for a container that size, huge drainage holes. Feeding like Peter says can let you have an old clump in the same container, provided the drainage is excellent, for 8 years or more without repotting.