Not a helpful or contributing post. Doesn't give any clear answer to OP.

Quote from jli

This is possible, but really if you're playing like this it means you're at some sort of last stand. i.e. you've pretty much lost. But anyway:
1. Click the garrison button.
2. Click the "miners out" button.
3. Select the units you want defending by holding down shift and clicking each one of them.
4. Press "U" to ungarrison these units only.

Well for me I make a box and press the buttons