Some Americans who bought homes or leased land were helpless when developers and brokers moved in. Ocean views can be fleeting. LA CRUZ DE HUANACAXTLE, Mexico — Doug and Dru Davis sold their San Diego County home several years ago to buy a $200,000 house on the beach here. The value of their new place not far from the resort of Puerto Vallarta increased fivefold — until some developers moved the beach. The couple's serenity was shattered last fall when construction crews began dredging the bay in front of their property to reclaim land from the sea. A planned marina,...