permanent job is fine. you can copy my offer:

来源: 于 2009-10-08 12:19:29 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次

We would like to offer you this position for a period of one (1) year, and desire to have you on board as soon as it is feasible, hopefully by Monday, August 29th, 200x. If we do find mutual satisfactory after one year’s work together, it is possible that this position be extended.