To get a tough rooster tender, you first pound him with a river rock. (after you kill him, please) :rolleyes:
Then you put him in a large pot with enough water to cover, and hold him down with the river rock. Simmer for enough hours to make the river rock tender. You then discard the rooster by feeding him to the dog and eat the river rock, which by now has taken on the flavour of chicken. laugh
Well this has been said before about how to cook a NZ Pukeko, so it ought to be the same with tough old roosters!

I think the secret to cooking non meat bird roosters is to stew very slowly in a crock pot. They don't have enough meat or fat on their bones to roast satisfactorily and will end up tough and dry.
You could also bone them out and marinade with kiwifruit and spices for 2 or 3 hours. Roll them up around stuffing and secure with skewers paint with a mixture of butter and olive oil and wrap in tinfoil and bake very slowly in low oven.