Five different Leinster players crossed the whitewash as D'Arcy and co ended the weekend in second spot with a 22-41 victory at Zebre.
However, the Irish side also conceded three tries meaning they had to work hard for their win in Italy.
And with Leinster also challenging for European honours with an Amlin Challenge Cup semi-final against Biarritz on Saturday, D'Arcy admits there is no margin for error.
"We know that our defence hasn't been up to scratch in the last two weeks so it is definitely in the forefront of everybody's mind," he told Leinster TV.
"Something we pride ourselves on is our defence so it is in everybody's heads and from the chats we've had we all really want to put in a good defensive display this weekend.
"We have been lucky in the sense that we have scored more points in those games but you don't want to be relying on that too much.
"The best way to look at things is you keep them out and score and take your chances is the kind of mantra we try and work off.
"We have probably had a few games this season where we have let a lot of points in but scored a lot of points as well. That is not always going to be the case so you don't want to be relying on that.
"We know we can score points but we also know we can stop teams scoring tries so it is a mental aspect."
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