Three Jack Russells?

by Elaine Millward
(UK)

I have two Parson Jack Russell's, and am thinking of getting another Jack. I have a dog and a bitch at the moment, both neutered, but have just read in my JR. book, it is not advisable to have two JRT's of the same sex, as they will fight.
My two present dogs get along brilliantly. Would it be a mistake to get another? I was hoping for another female.