SANTA CLARA, Calif. -- There's no secret about what the NFL's second-ranked defence wants to accomplish over the second half of the season.
It's the same list of things the first-place San Francisco 49ers got done on that side of the football during their first eight games.
"As a defensive unit, the way we play speaks for itself," outside linebacker Ahmad Brooks said Friday. "We're an aggressive D, and we want to shut guys out."
Nobody in the league does that better than the 49ers, who have allowed fewer points than any team and rank either first or second in the NFL in seven defensive categories as they prepare for their first game since their bye on Sunday against the St. Louis Rams.
The long layoff -- San Francisco will be playing just its second game in 24 days -- gave the 49ers some time to reflect on a defensive performance that was dominant during most of the season's first half.
The 49ers, who returned all 11 starters from last season, have matured as a veteran unit, building on what they accomplished in 2011 when San Francisco ranked fourth in the NFL in total defence and led the league in rushing defence.
"It's a veteran group of talented players, and you see upward trajectory really in all their play," coach Jim Harbaugh said. "I don't see anybody that's falling off or decreasing in their effort or their performance on the field. And then how they're playing together as a group -- all those things -- we're seeing good improvement at a high level."
The 49ers (6-2) have played at the highest level keeping opponents away from their goal line. San Francisco has allowed a NFL-low nine touchdowns, including a league-low six through the air.
The 49ers have not allowed a touchdown in four of their past five games, and their opponents have scored just 12 total points in those four victories. San Francisco shut out the New York Jets in September and is allowing just 12.9 points per game, which would be a franchise record if it holds to the end of the season.
San Francisco's lone shutout last season came against St. Louis at Candlestick Park, where the 49ers will be looking to shut down the struggling Rams (3-5) again and extend their 11-game home winning streak against NFC West opponents. That's the longest active streak in the NFL.
"You want to be good at everything, but the biggest thing is keeping teams out of the end zone," Harbaugh said. "Number one is keep the other team from scoring, as few points as possible."
The 49ers also have made strides this year defending against the pass, which has made them a complete defence. San Francisco ranks second in the NFL in pass defence after finishing 16th in that category last year.
San Francisco is the only NFL team not to allow a passing touchdown of more than 20 yards this season, and the 49ers have allowed only nine passing plays of 25 or more yards, the third-fewest in the league.
Defensive co-ordinator Vic Fangio has lauded the improvement of his starting secondary, which includes Pro Bowlers Carlos Rogers and Dashon Goldson, and also nickel cornerback Chris Culliver, who has become a regular part of San Francisco's defensive packages.
"Little strides in a lot of areas equals a big difference," Fangio said.
One area where the 49ers would like things to be different the rest of the season is creating more turnovers. The Niners led the NFL in takeaways (38) and turnover differential (plus-28) last season, but at midseason this year they've produced only 12 turnovers and their turnover differential stands at plus-3.
But there's still a half season to work on improving those numbers.
"We were looking at that turnover-ratio chart the other day," Brooks said. "Last year, we were at the top of that chart. We're going to have to boost that up. But we'll just keep doing the same things we've been doing all year, the same things we were doing last year, just trying to go out there and dominate the other team."