ἐκείνων τῶν ἱππέων: So far, JM, you seem to have a lot of difficulty distinguishing singular from plural in all declensions. Very soon now, you'll want to learn the declensions and learn the difference. And it can make a big difference: here, for example, there's a world of difference between a single horseman and a whole cavalry.
ἐκείνων = "those" (genitive plural masculine)
τῶν εὐδαιμόν: did you mean to write τῶν εὐδαιμόνων?
ὑπέρ τοῦ φυλάξασθαι = "for the purpose of avoiding" (infinitive used as noun)
ἀρχὴ, "government": don't confuse with ἀρετή, "excellence."
Give it another careful try, champ. You can do it!