I got my hard achievement for The Dig mission last night [destroy 50 Protoss structures] without having the ability of scanner, nukes or flying units.
Strategy is to build 2-3 barracks and fly it North of the Protoss base using the terrain advantage to reveal the structures.

Got a question for you guys, can enlightened me how to issue multiple commands for the dig laser? I tried Shift+click on the protoss units and i can see it set a waypoint in sequence but after that, the laser didn't fire. Then i tried Shift+Right Click and still not working. So ended up manually targeting the units one by one. Appreciate your help.
Thanks.