Slowly go up to a Wall Mine. It will flash red and green at an even pace. To disable this, you have to press Action when it flashes green. If it becomes red the instant before you press Action, it will explode. The way to always do this safely is to hold Action button when the "Disable Wall Mine" selection appears. Then, if it is green, release the button. If it is red on the screen, move the selection up to "Back To Game" and try again.