The alternative :
A.) See how much you can break that read - writeable dmg file from another account.
(you could try setting the rights of the files of the folder, so that only you,the owner may write to the files. Everybody else just read, That may help!
That way, your image is “safe” even if it is writeable, at least that is what I suspect. Also make the image just big enough to accomodate the .DS_Store file, which you also set as yours, and only readable.
B.) If you can break it, set normal read-only rights from finder, in your normal account, but keep the dmg-file read write able.
See how much havoc you can make.
C.) If you can break it still. Read up on Access Control lists, and set Access Control rights. From your normal account, try it on the “Gangster” account.
Start over until your files are secure.
Somewhere along this path, you should end up with an untinkerable dmg-file, that opens in listview, in a finder window.
That may work. I’d at least try it.
Telling people, that you are sure they won’t remember something, is a very good way of making them remember!
This is a lot of fuzz, when you can only press cmd-2 in finder. On the other hand, if it is a product, even if the product is just datafiles, then it is ok, to at least show customers that you are able. And the Customers are usually right.