Neopolitan Mastiff, How are they?

My husband wants a Neopolitan Mastiff. I am not familiar to the breed and have been researching it but havent found my question to it really. We will be getting land soon of about 3.4 acres and I was thinking of turing 1.5 acres into a dog only area as I have horses also. I also have a 10mnth old Shiba inu dog, my question is will a Neopolitan Mastiff get along with another male dog when it gets older, or will it try hurting my dog? we had problems with our mini dachshund we had to give back to my mother inlaw because It would attack my dog and bite through its ear like it did to his own father when he went back to my mother inlaw. I am just worried about dogs saftey and dont want to get another mean dog to hurt it. Thnks and if you have any good breeders I can talk to about the breed I would love the info!!