Right now, mines after being spotted become useless and become a problem for their owner, as without either suiciding your ship at them/getting new naval warfare level, you cant place new ones. I think about this solution:
After being spotted, mines still can damage any enemy naval unit if its in an adjacent hex, but this time with 33% chance, not 100% as with unspotted. This would require to go around them even more, or use your unit to take damage so that the assault can continue, for example in adriatic.
To balance this, mines should disappear after 2/3 turns at the end of the turn of player who placed them. This would give a window of opportunity for enemy to exploit, and incentive to go regularly out in the sea, and would provide interesting engagements.
What do you think?
Down-side to this is that it would require continuous placement of mines, and also risk making them OP.
I haven't checked but it is it really not possible to simply disband the mines?