Darren Moore believes his defensive unit deserve credit for their work done so far this season.
Rovers have conceded just eight goals in nine games in Sky Bet League One, with only top of the table Ipswich having let in fewer.
He said: “There are areas of the game that as a squad we’ve improved on as the season has progressed and the defensive area has been one of those.
“We’ve done plenty of work on the training ground and it’s pleasing to see that we’ve tightened things up.
“That comes with the continuity and players playing together regularly as well as knowing what is expected of them.”
Portsmouth are the visitors to the Keepmoat Stadium this weekend, and Moore is expecting Kenny Jackett’s side to provide a stern test.
He added: “They had a tough end to last season and it’s been a quick turnaround for them to go again but they’ve recruited well.
“I would imagine the expectations are high down there so will be looking to improve on the start they’ve made.
“They have some really good players and one of the most experienced managers in the division so we know we will have to be at our best to get a result.”
