In English, it means: it's too hard.
Ne travaillez pas trop dur.
too hard
The feminine word for "dur" in French is "dure."
A hard work is un travail difficile / un dur travail in French.
hard
plus dur
dur / dure is the French adjective for hard.
dur, dure
Dur
The song itself is in the public domain, but certain arrangements, performances, and recordings may have their own protections.
It depends whether you are speaking informally or formally Informally, you would say: ¡no trabaja demasiado hoy! Formally, you would : ¡no trabaje usted demasiado hoy!
a banana that play the french horn dur