ETA:
A number of studies have been done & published which highlight negative aspects of spaying & neutering your dog too early. There are hormones in the sex organs that regulate growth & muscle development. When dogs are fixed before they are done maturing, it can cause physical problems in many different ways (doing a search online can provide more information that I can try to put in this post).
I recommend to puppy owners that they wait until the age of 2 years. For people who do not think they can prevent an accidental breeding, there are some vets that will now do a vasectomy procedure on male dogs.
Neutering does not alter behavior, but if done in males before they reach sexual maturity, they will act out in other ways. If you do not have problems with your dogs behavior, chances are you wouldn't have had marking issues if you had not neutered your dog.
Original response:
I am a breeder with 2 intact males & 3 intact girls living as house dogs. I have NEVER had anyone mark in my house. The only urination that has occurred is by accident, & very infrequently at that.
First, regarding the issue of your boy marking in a house he is visiting. If they have dogs that mark, yours will do the same. Chances are if he travels to a house where there has not been marking, he will not take the liberty.
Secondly, if you have a male dog & are having difficulty in housebreaking & teaching non-marking behaviors, you should probably take a look at your own behavior around your dog. For some reason, it sounds like he (& other people's males) think that they are "top dog" & therefore have the right to mark.
There are right ways & wrong ways to assert yourself with your pack, and the best advice I have is to work with an animal behaviorist who can meet you & your dog in person. Some breeds can be more territorial than others, & then there are definitely more expressive personalities in some males than others!
It sounds like you do not have a problem now, but something to consider for your next pooch. In addition, you can also get "belly bands" for dogs to wear, so that if they do attempt to mark, it is absorbed by a pad instead of sprayed on the rugs/furniture.
I will add, 4 of my 5 furkids were born & raised in my house, and successfully housebroken without much trouble... considering that they spent their first 10 weeks being told it was OK to pee in the house, that's not too bad!
Hope this helped answer your question!
T. (Breeder/Trainer Rhodesian Ridgebacks)