Apartment Guru: Peeping Tom Prevention

Dear Apartment Guru,

My neighbor and I have adjoining balconies separated by a wall. He has a little dog that easily slips through over to our side. Whenever this happens, the neighbor proceeds to crawl over the wall to fetch his yappy dog. Sometimes my roommates and I "entertain" in our living room (not at the same time), into which this guy would get a front row view if the timing was right. Plus it just feels weird that he keeps coming over the wall like that.

How can I tell him to stick to his side without ruining the neighborly relationship, or accidentally drop-kicking the dog off the balcony?

-- Not Sure How to Rap About the Yap