Remember that V's are very sensitive and eager to please, so if you catch him marking inside, you want to get in his face and yell "NO!", so he "Gets it"..your displeasure....you can tell when it's "Just right" b/c he will immediately tuck his tail, bow his head, and probably flick the tip of his tail, maybe even roll over. Don't over do it or over correct.
Again, at 9 months, this isn't a hormonal thing just yet, so I'm concerned that the whole topic is somehow being raised by your trainer. Always use common sense with your dog, regardless of so called "experience" or self importance of the person giving the advice or recommendation. You know your dog much better than anyone else, so if someone..even someone with credibility and authority...suggests things that just don't seem right, do not do them. To me, a trainer who is "pro" or "anti" anything and makes that a part of the training is a trainer to be very wary of b/c their techniques and recommendations aren't so much the result of their understanding of you and your puppy, but rather some preconceived notions that they then apply to you.
In short, at 9 months, you train a dog..especially a Vizsla.. the same way and with the same techniques regardless of which genitalia they have and their absence or presence, what you see is not the result of hormones just yet.