Here's what did work, though--changing the windows effects settings through compiz:
1. sudo apt-get install compizconfig-settings-manager
2. Run the compiz config manager: ccsm (no sudo)
3. In the compiz config manager: General (left side) -> General Options (right side) -> Key bindings (tab) -> Show Desktop (with the keyboard icon) -> Click the "X" icon (on the far right) This sets the default of <Control><Primary><Super>d.
4. Click on the key binding <Control><Primary><Super>d.
5. Click "Grab key combination"
6. Press ALT+D (or whatever other key combo you want to bind to the "show desktop" option).
7. Click OK
8. Click Back
9. Click Close.
10. Restart your remote session if you have one running.
That fixed it for me.