oh i thought you wanted to do something else.
like create some sort of on screen display...
but parenting gives more controls, instead of constraining. you can still key frame rotate values, or create a more elaborate heirarchy, make lods based on distance etc...

the first part show constraining, which locks your rotate values. the second shows parenting, which you are free to move scale object or rotate. or script to be overdrawn on screen, so there is no clipping.
https://www.vimeo.com/1525686