The Dolphins continued to address their need in the secondary by signing free agent cornerback Will Allen to a four-year contract, finishing what essentially was a trade of cornerbacks with the New York Giants. Allen received a $12 million deal, including $5 million in guarantees for a roster bonus and signing bonus. Allen can earn another $2 million in incentives. Agent Tom Condon confirmed the signing and said the Seattle Seahawks and Kansas City Chiefs had expressed interest in Allen before he visited Miami on Friday. ''Will's very happy,'' Condon said. ``It's a good situation for him.''