Cornerback play and special teams coverage were on the top of coach Jim Harbaugh's happy list Monday.Both units came up big in the San Francisco 49ers' 34-3 win over the Houston Texans on Sunday night.Tramaine Brock, the No. 3 cornerback, had two interceptions, including one he brought back for a touchdown. Special teams suffocated Houston just as it did last week on the road against the St. Louis Rams. The group is much improved from last year.