▲两个都不太合适。因为“Once a thief, always a thief”和“Once a beggar, always a beggar”都是用来介绍身份特点，侧重于描述；而“一日为师，终身为父”往往被用来教育学生尊师，所以它侧重于来阐述责任和义务，有点像祈使句。

▲建议的版本：

Always respect your teacher as you do your father.

或 Students should always respect their teachers as much as they respect their fathers

▲附老外解释的部分摘录：

Neither of them works because the original idioms are all about the named person always being the same through their lifetime.You are talking about how someone should treat their teacher. This is different. 

Maybe, something like "(One should) Respect your teacher as you do your father."

▲个人认为：翻译不能总是一一对应。译者要必须把一个语言文化中的某个意思，以一种自然的、人们喜闻乐见的语言形式，呈现在另外一个语言文化中。