You know, I heard that somewhere, too... Can't remember where.... I haven't had a huge sample of chicks I've tried to train w/ "negative reinforcement", I just know the 4 Roos I hv now are "nicely" vigilant but avoid me (which is fine). I'm hoping maybe it's cuz I "nipped it in the bud" they were but a few weeks old. I also know (as I'm sure ya'll do), too, that fighting with an adult roo only makes him worse!! I wonder if there's any correlation between fertility and aggressiveness? Cuz I am not going to keep a roo with a bad temperament.
Almost started a new thread on BYC to ask if people have noticed that the bigger the comb the more aggressive the rooster - and oversized comb - watch out.I'd be willing to bet that more testosterone equals more aggressiveness and higher fertility.

I have to say I took a page from sweetdreaming's book - and I really appreciate the squirt bottle technique. I only use plain water...and I feel no remorse if a rooster appears like he will/may get out of line just squirting the heck out of him right in the face and not relenting until he is high-tailing it to elsewhere. -- It really works for a long time. All the other rooster techniques I tried with all the roosters were only temporary, seemed really time consuming -- (carry him around while you do the chores, rub his face in the dirt in front of his hens, try to out rooster (dominate him) -- show him you are the alpha etc.) were really only very temporary at best, seemed needlessly cruel and ineffective. I hang a squirt bottle on the fence and sometimes if I feel I need it , all I have to do is shake the bottle. LOL..... I think that this is something that works well and it doesn't harm much more than the rooster's pride. I like it!
Also, I wonder if age of the rooster has anything to do with it.
Right at this moment, I have 4 adult CL roosters out there crowing - (and one blue Isbar in here crowing - it's very musical around here this morning)--- Each Legbar is looking out for his hens.
Now I notice that my 1-week old baby - the one little cockerel is showing the same behavior -- he is patrolling - he is standing just outside the warmer -- keeping his eye out for danger...really showing rooster behavior IMO - as a tiny tot. Wonder what he will grow up to be.