Warning: PG-13 post ahead!

I have a weird question. How often do neutered males exhibit sexual behavior?

Jack is just over 2 and was neutered at 6 months. He had just started lifting his leg to pee right before he got neutered, and was still at the puppy state where he greeted other dogs by sniffing/licking their mouths rather than sniffing the backside as adults do. He had exhibited absolutely no sexual behavior, and from what I could tell (and I have limited experience with such things) he had not yet reached physical sexual maturity.

Like many dogs, he will occasionally (not often) try to mount another dog during play behavior, especially if the other dog is clearly subordinate to him (a smaller dog, for example, or one that is getting old). I generally put a calm stop to this unless the other dog is a well-known buddy and they don't mind the behavior and mutually break it off quickly. Once he tried to mount a three-legged beagle, and I thought that was just crossing the lines of rudeness! LOL, so I immediately told him to "leave it."

However, this spring we were at the park (not a dog park, just a regular park). There was a trainer there that we know, with a Golden, and another woman with a young Golden female we had not met. The woman was a breeder, and the female was entire as she was planning on breeding her (gorgeous dog too, but that's neither here nor there). It's a very quiet isolated area of the park, and our dogs were off-leash playing.

Well, it's the first time we've met a full-grown un-spayed female, and Jack acted in a way I've never seen. I asked the owner if the female was in season, and she was not but she felt she might come in soon (her littermate sister had just been bred.)

Jack was quite literally drooling like crazy, the way he normally does only when treats are in the vicinity. He was pretty obsessed with her, and he did try to mount her but not in the way he normally does when he's play-mounting another (usually male) dog. I kept him away, and he's pretty well-behaved so a few stern "leave its" and some well-timed efforts at physically getting between the dogs stopped him. Then we all leashed our dogs and were on our way.

I was surprised at his apparent level of sexual interest. The other Golden was a neutered male, and he showed absolutely no interest in her. The female was young and had not been bred, and she seemed not bothered by the whole thing (I know sometimes females who are not in season will quickly chase off an amorous male).

Jack also is a prodigious marker (never inside, but outside whenever he gets half a chance) and will stop to mark (it seems) every vertical object in his path if he is not on heel.

I understand that neutering does not stop typical male behaviors in all dogs. How common is this? He shows no other "negative" male behaviors; he is not dog-aggressive, he is no more territorial than I would expect from the breed and happily welcomes other dogs (even males) into the house. So I'm not actually concerned about this, just sort of curious.