Leave them the way they are
Limit the max number of mines
Nerf damage or require higher upgrades
Increase build time
Increase visibility
Increase cost
Don't pay out for nuke kills
Increase RU leeched from mines
Give mines a time limit or drain HP (must rebuild)
Limit number of mines per player
Apply limits only during overtime
Display effect on hit (Higor)
Make Rocket Launcher detection highlight it (Higor)
Reduce HP