The Germany international was snapped up by Wenger before the transfer window closed to bolster the club's defensive option.
The experienced defender turns 27 this week and the French tactician feels he is now beginning to show his true form.
"Per is getting stronger and stronger," said Wenger.
"He is calm, intelligent and he is now showing clearly that he can lead the defence."
The former Werder Bremen defender is encouraged by Wenger's praise.
"If the coach is praising me, that is of course a great thing to hear," said the 76-cap international defender.
"But I have to keep working on things, I know I can play even better. I want to put in some good work, especially on defence, that's my job."