Safest field to use for md5 storage

Hi which field are unlikely and never to be used any all programs? so I can use it for my md5 storage.. I was thinking of using either the copyright or comment field..

Note I don't want to create a custom field because I did it before and editing meta data using windows explorer wiped that field.. I learnt it the hard way..

I am equipped with very limited clairevoyant abilities.
So I am not able to say which turns the future development of players will take and which of the standard (as in "can be used by everyone") fields will be used.

What I can say: it is rather short-sighted to use the Windows Explorer with all its limitations as tagging program. MP3tag is the program of choice for this purpose.

See the help for a list of supported fields:
http://help.mp3tag.de/main_tags.html

Or you write a little tagging program of your own and use the PRIV field which can only be handled by the originating application. It is a standard field but is usually ignored. And as standard field it won't get deleted by WE.