The Gunners, currently away on a training camp in Austria, failed to stay the distance in the last title race as lapses in concentration at the back proved costly.
Arsenal leaked 41 goals – nine more than champions Chelsea and 13 more than runners-up Manchester United.
Djourou, however, insists that is all about to change, as the Swiss international prepares to return from a long-term knee injury.
“It is true that 41 goals is too much when you are playing for the top places,” he said. “I think sometimes we are missing a bit of aggression.
“It is not that we are not good enough. We have top players at the back, top players all over the pitch. It’s just that we have to be stronger as a unit.”
Centre-back Djourou missed almost the entire campaign last season, playing just once against Fulham on the final day.
But Djourou, 23, is ready to battle summer-signing Laurent Koscielny for a place alongside Thomas Vermaelen at the heart of the Gunners defence.
“I played 90 minutes last week and it went well,” said Djourou. “But I have to play more games and hopefully I will be ready.”