1. Landlord leases a commercial property to a private childcare center. To comply with child safety laws, the center builds a chain-link fence around the playground. Landlord drives by the property and notices the fence does not comply with the zoning code, subjecting him to penalties. Landlord talks with the center's director and says he understands the center's need for the fence. Based on this conversation, the center takes no action to change the fence. Four weeks later, landlord sends the center an eviction notice because of the non-conforming fence which violates the terms of the lease. What remedial defense would best assist the center?
   1. Estoppel.
   2. Laches.
   3. Unclean hands.
   4. Unconscionability.