However ... be forewarned! ... the longer you wait to neuter your dog, the far greater the chance that he will continue to mark for the rest of his life, even after he is neutered. That is because, even though the hormones are gone, the HABIT if formed.
VERY TRUE!
I know this sounds mean, but I can't stand to be around unaltered males! They are so gross!
I AGREE 100% and it is not only the marking, it is the excess "sexual" energy, the constant licking (and not the kissing type, the DISGUSTING type).....etc.

Do what you must, but if this dog is not in the top 98 % of his breed (i breed standard) then he need not father puppies.