Mont. Code Ann. § 71-1-209

When a grant of real property purports to be an absolute conveyance but is intended to be defeasible on the performance of certain conditions, the grant is not defeated or affected as against any person other than the grantee or the grantee's heirs or devisees or persons having actual notice unless an instrument of defeasance, duly executed and acknowledged, has been recorded in the office of the county clerk of the county where the property is situated.