Del. Code tit. 12, § 613

If the property interest being disclaimed is an interest in real property, the disclaimer shall be acknowledged in the manner provided for deeds of real property. The disclaimer shall not be valid as against any person, except the beneficiary, the heirs and devisees of the beneficiary, and any other person having actual notice of the disclaimer, unless an original thereof, or an attested copy thereof if the original is required to be filed elsewhere, is recorded in the office for recording of deeds for the county or district in which the real property is located.