The Sierra 10.12 version of Disk Utility lacks many features that were available in earlier versions.
For instance, users can no longer choose from a number of presets when creating a blank image (dmg) file. A default setting of 100 mb is provided, which the user can overwrite and change.
Also, the ability to burn discs from the program has been removed. Finally (and this change happened in Yosemite 10.11), the ability to securely erase disks has been removed as a menu option and must be done using a command sequence in Terminal.
Secure Empty Trash (per OSX Daily):
Type the following syntax exactly and be sure to include a space after the flag:
* To delete a file:
* srm -v
* To delete an entire directory:
* srm -rv
Now drag and drop the file or folder you wish to remove into the Terminal command line, this will fill in the complete path to the file automatically.
If you are uncomfortable performing the above steps using Terminal, you may want to hold onto a machine running an older system like Mountain Lion (10.8).