Depth is the enclosure
For a fossorial tarantula, deep compactable substrate is not optional decoration. It is the core of the habitat. A shallow enclosure forces a burrower to remain exposed and removes one of the behaviours the animal is built to perform.
Starter burrow
Provide a cork edge, angled bark or pre-started tunnel so the spider has an obvious place to begin. Many species will enlarge it dramatically. Once the animal has committed to a burrow, avoid digging it out to check on it.
Moisture below the surface
Many fossorial species benefit from deeper moisture even when the surface is comparatively dry. Add water to one area or overflow the dish as appropriate rather than soaking the entire enclosure.
Feeding a hidden spider
Offer prey near the burrow entrance and remove it if ignored. Do not force prey deep into a sealed burrow. A spider that has closed itself in may be moulting, fasting or simply choosing privacy.
Observation
A fossorial enclosure can still be enjoyable if the burrow is encouraged along the side of the container, but visibility is not more important than security. Do not redesign the setup every time the spider chooses an inconvenient tunnel.
Maintenance and rehousing
Most maintenance can happen at the surface. Rehousing should be planned before the burrow is opened because an exposed Old World fossorial can move extremely quickly. Use containment and a catch cup rather than hands.