Hey Zak!
Thank you SO MUCH for the review! Its the first time I've been able to watch someone play my game, and it was eye-opening. I've made several notes about things you mentioned, and things you tried, and will be adding improvements to the game.
By the way, the engineer's put up walls on the rock cubes, but that doesn't prevent the cube from being mined. Walls and floor tiles are just for decoration, just to make it look nicer.
Thanks again! I may ask you for help again in a few months :)