For the fourth consecutive year, merit pay increases for exempt, salaried professionals are expected to average 4.1% next year. One reason is that 90% of the companies that were surveyed by Buck Consultants Inc., New York, are using one or more alternative reward strategies. The two most used rewards: hiring bonuses -- used by 75% of the companies, and retention bonuses -- used by 45% of those surveyed. In addition, one-third of the companies surveyed offer broad-based stock plans, with another 12% in the process of implementing them or considering their use.