Roosters are helpful in alerting the hens of a predator's nearness but even the best rooster can't keep you from losing an occasional hen. What were the circumstances of your chickens being killed? Were they free ranging or in the coop or run? There may be additional steps you need to take to keep your chickens safe.
If you free range a rooster is great, he keeps them togeather and there 8s safety in numbers. But that is really as far as a roosters protection goes. If you are having a predator problem a rooster will not help you much, he will just be the first to die.
If they are free range you need a good dog, or two. If it is an option a fence, electrified, would even help more.
Welcome to BYC. Glad you decided to join our flock. The other members are correct. No rooster breed on the planet is going to be able to fight off the larger and more dangerous predators such as large dogs, coyotes, wolves, bobcats, raccoons, eagles, etc. The rooster will just as likely fall prey to them as the hens. If you are free ranging your flock in an area with these kind of predators, you are going to lose some of your flock. It's up to you of course to determine whether or not those losses are acceptable. If not, then you need to keep you flock in an enclosed coop/run that's built like Fort Knox. Be sure and use hardware cloth rather than chicken wire and if you have coons in your area, make sure that you use a padlock or at least a double action latch on your coop door as coons can easily figure out how to open a single action latch. Please feel free to ask any questions you may have. We are here to help in any way we can. Cheers.
The best a rooster can do is sound the alarm so the hens run and hide, or fly off. You may do better with guineas - they sound the alarm quite loudly and with some preds like snakes, they will mob them and either escort them off the property or kill them. Of course guineas sound the alarms often for real as well as imaginary enemies.