1. Install a retaining wall. This is the most effective way to prevent a clay cliff from collapsing. A retaining wall is a structure that is built to hold back soil or other materials. It can be made of concrete, stone, or wood.

2. Plant vegetation on the cliff. This will help to hold the soil in place and prevent erosion. Some good plants to plant on a clay cliff include:

* Creeping jenny

* English ivy

* Periwinkle

* Virginia creeper

* Wild strawberry

3. Cover the cliff with a layer of mulch. This will help to keep the soil moist and prevent it from drying out and cracking.

4. Water the cliff regularly. This is especially important during dry weather.

5. Avoid placing heavy objects on the cliff. This could cause the cliff to collapse.

6. Inspect the cliff regularly for signs of instability. If you see any cracks or other signs of instability, contact a professional engineer or contractor immediately.