SANTA CLARA, Calif. -- Through five games, the San Francisco 49ers' emphasis on improving the coverage units on special teams has been a success.The unit is allowing 21.4 yards per kickoff return. Last year, it gave up a whopping 26.9 yards per return. Against punts, the 49ers are strong as well, allowing 7.4 yards per return.The unit was particularly strong the past two weeks, at St. Louis and against Houston. Monday, 49ers' coach Jim Harbaugh heaped by praise on the unit.