Mining is itself an Undermining action, so you can just do it straight back. One of the biggest undermining actions last cycle was done almost entirely through mining.I'm sure this has been said many times before but.... mining is way overpowered, especially compared to the little that can be done to undermine it.
It's also extremely situational because of the location requirements and the need to establish a favourable BGS state for selling. Sure, when it works, it's great, and it's a big galaxy so you can always find somewhere if you're just in it for the personal merits. Now try mining to reinforce a system with no ringed gas giants, a single rocky asteroid belt, and a lack of Refinery/Tourism economies.