Puppy Behavior Confusing Me

Okay everyone - new to this forum. Looking for some insight into a new behavior my puppy has developed. Long story short.. I have two miniature schnauzuers (male 4, female 3 - both fixed) and about 4 months ago, we added a male Maltese puppy to the family - he is now 5.5 months old. They all three get along fabulously, with only the normal play fighting (tug of war with a toy, chasing each other, etc. ).. Recently, my Maltese pup (not fixed yet) has been sniffing the rear of my female schnauzer.. and does this smacking sound and motion with his mouth after he has gotten his sniffs in.. then he has hiked up his leg to pee on her (on three of the four occasions I witnessed).. I know this may be marking his territory or something of the like.. but I can't understand why he would do that ON her? Any ideas??? :confused:

Bad aim perhaps. :) He could just be aiming it in her direction, not trying
to spray on her. He's old enough to be neutered & that should help.