He's marking! How old is he currently?
Neutering will DEFINITELY help.
I'd get him fixed asap. Besides marking, it generally makes for an all around better dog. More loving and affectionate it will sometimes make a male (it did for Jackson) and it 100% reduces their risk for testosterone cancer, it makes them not wander so much looking for a female in heat as they would being un-neutered when he becomes fully mature. It will also help with future or current aggression. It usually stops humping if done early enough and reduces the chances of that wee-wee constantly popping out, lol. I totally believe in spaying/neutering our animals as pet owners.
Do your research and decide what you think is best.