We have had to neuter two of our older patrol dogs due to prostrate problems. I also worked with another handler w/ a neighboring dept. that had to do the same.
All the dogs were older critters (6 and up). I would say that since it is major surgery only do it with an adult if it is necessary. Too much risk other wise.
We saw a loss of the edge on the dogs in general. But, was it due to age plus an added insult with the surgery?? or was it neutering??....it is hard to know.
I also have had some labs neutered due to marking...they were dope dogs and it really didn't change their behavior much, maybe a little.
What has worked best is to teach the dogs that mark that it is not acceptable to mark. I have the handlers take the dogs to places they know that have lots of dog smells and lots of dogs in the area. they teach the dogs an encouregemnt to pee and poop. When they start their outing they take them to a place to be encouraged to do their thing. Then they go for a walk. ALL doggie behavior are met with serious punishment. No marking, no eyeing other dogs, no attending to barking, nothin'. They are corrected for thinking about doggie stuff.
Since this is not in the guise of working (deployment) it doesn't effect their performance. But, once they can walk in strange neighborhoods and not mark, sniff, of pay any attention to other critters it boils over into not doing it during deployments.
My current youngster (Franko Fasanerie) was a marking fool at 12 months. No longer does he even think about it when we are out and about doing the work.
Too often handlers think that they will take away the dogs drives by crawloing up their butt for these behaviors but if you make it clear the only behaviors that will diminish are the ones that are getting in the way of the work and you will see the hunting and searching behaviors actually increase since the dog is no longer weighed down by the baggage of doing doggie stuff while out working.
Now a little caution: I worked with a guy that would use the nick on his e-collar to correct his dogs marking behavior. One of my more frustrating experiences was watching him miss the the timing so badly that the only thing the dog learned was to hurry up the marking behavior!!! Piss a bit really quick or get it was his game. he got really really fast at lifting his leg and squirting a drop. Handler just couldn't seem to get it that he had to be AHEAD of the actual marking behavior with the punisher!!!
It is a little easier for the novice to do it on leash with a no or fuey (or I growl at my dog for such behavior) before adding e-collar work to it. Then quickly tying in an apprehension or find into the work once the dog goes back to working after the punisher.
Often the e-collar won't even be needed if you identify the character trait that leads to marking.
Often the marking will go away as you assert your role as dominant character in the dog-man relationship as well.