There is nothing you can do about crowing. It's natural. That's why many people keep hens without a roo. As the roos get older and more protective, they can get very aggressive, and, depending on the breed, you may have to get rid of them. When their spurs get big, you have to watch out. RIR's , for instance, can get very mean. Get a really strong squirt gun and keep it handy. At any sign of aggression squirt the bugger in the face real good. They hate it. And he will learn, hopefully.

I just had the experience of visiting a working farm where they are winnowing down the roosters based on size and dominance and have so far narrowed it to about six, who are CONSTANTLY crowing at each other, making me appreciate the traditional solution to this issue. Not to go all red queen on you or anything, but I honestly think that decapitation is the simplest solution. Unless you are planning to breed, why bother?

I've heard you can stop them from crowing by putting them in a cage which is too short for them to do the stretch they do when they crow. Nothing you'd want to do in the day, but maybe at night?

I also knew of one person who caged her roosters in the basement of her house at night. They heard crowing through the air ducts, but the neighbors didn't, and all wondered how she "trained" roosters not to crow until 9:00 (when she took them outside).

I found an article that was in the NY times archives from 1934 about surgically de crowing a rooster by clipping one of it's vocal cords. I've not be able to find it again. I live in the city and we're not allowed to keep roosters. My WYND just let out his first crow last night right after putting them in. I've not had a chance to build my coop yet, and so we've just been putting them in their brooder box at night which I've added perches too. They seem quite content as "house chickens" as they just come up to the back door and start clucking for me to let them in. It's actually quite comical. We're getting ready to move to around Houston / Pearland TX area. My sister says they don't have CCR's there and it's somewhat farm like anyway. So we should be able to keep him. But I don't ever want more than one roo at a time unless I have plenty of space and hens.
Cheers,
James