I want my Mac running Sierra, to stop hiding dock when I enter "Command+Option+D"

1. Click on the Apple menu
2. Open "System Preferences"

3. Select "Keyboard"

4. Click "Shortcuts"
5. Select "Launchpad & Dock"
6. Uncheck "Turn Dock Hiding On/Off"

You can edit the keyboard shortcut by going to System Preferences app → Keyboard → Shortcuts → Launchpad & Dock and assign a different non-conflicting shortcut for toggling Dock display.

Go to System Preferences/Keyboard, From there select the Shortcut tab at top of window. The 1st option on the left is LaunchPad and Dock. When you select that you see an option to make control-command-D a shortcut for Dock, Uncheck that option.