When big-box retailers close, other tenants look to shift or end leases. Vacant big-box retail space in shopping centers throughout metro Denver has left many neighboring retailers combing through their leases and looking for a way out. Many retail leases contain provisions known as "co-tenancy" clauses. The clauses take many forms, with some requiring a certain percentage of a shopping center to be leased and others naming specific retailers or categories that must remain open. If the conditions aren't met, the remaining tenants in a center can demand rent reductions or leave altogether. In other cases, tenants who are preparing...