Marbles or rocks in the waterer! Mine tried to go swimming as soon as they were in the brooder. When they are juveniles it would be a good idea to separate them into breeding groups or at least dole out the females with separated males. My alpha juvenile just killed another male the other day with well placed kicks and I wasn't expecting it at all because the girls aren't even laying yet. To me sebrights are something else- nothing like ANY of the other large fowl or bantam breeds I have.
That just brought up a topic I have been thinking about. I have a lone Seabright pullet. My DH was asking if we should get a roo to go with her. I have plenty of bantam roos ( d'Uccle, D'anver,Silkie...) just no Sea bright yo go with my girl I rescued when my friends coop flooded. I have read were the roos are aggressive to each other, but are they to people as well?