I don't think breeding is a "touchy" subject on this site
But it is one with some very clear rules - the only way breeding will be promoted on this site is responsibly
and for the betterment of the breeed, or not at all. We even set out in the site rules what that constitutes.
If you want to breed your dog, you need first to know whether doing so is going to improve the breed and whether or not it would do harm. You can't produce good quality boxers by breeding from dogs that are not close to the breed standard, therefore you have to have that assessed. That is what the show ring exists for (the ONLY thing it exists for). So, have you shown your dog or otherwise had him assessed for his conformance to the breed standard by someone qualified
to make that assessment (eg. a judge)? If not, you should not even consider breeding him until you have.
How about having his hips x-rayed for dysplasia, heart ascultation to rule out aortic or sub-aortic stenosis, holter monitor exam for signs of cardiomyopathy, and thyroid panel for early signs of hypothyroidism?
Well, I don't actually expect that you have done any of those things. Why would you if you didn't buy your dog with the prospect of becoming a breeder in mind?
But the point here is, you can't actually responsibly use your dog for breeding until and unless you DO do all of those things. Otherwise, you risk being responsible for the production of puppies that may suffer some serious genetically inherited diseases (and those conditions are NOT rare - not in the least). The sort that will impact significantly on the quality and/or length of life of any affected pups. More info. at www.boxerworld.com/health_testing
Are you really prepared to go to all that effort and expense just so someone else can use your dog as a sperm donor?
Incidentally, to answer your question about the marking: Yes, a dog that is used for breeding is far more likely to mark than one that is not bred. That may or may not include indoors. A dog kept intact is also far more likely to suffer from a range of health conditions later in life. More information about that at: http://www.peteducation.com/article....&articleid=911