nate, Miss Lydia is right. while a pea could do a lot to defend itself and its hen it would either be killed outright or mortally wounded by a fox. Google "can a peacock kill a fox" and check out what they say. Keep your peas safe just like you do all your other birds.
Maybe not kill it but scare it away bc i have a bird dog that almost killed a chicken on accident and my peas attack her and now she is terrified and my geese defended my ducks from a chicken hawk it attacked a duck and my geese jumped on it and seriously scared it bc it hasn't ever came back im not saying they will kill it but could defend themselves im not trusting anything around my birds but they are good protectors if i would here ANYTHING i would grab my gun and go out there