[Commander G2]

As a refinement of the mine strategy suggested by others, consider making a cheap mine with only one warhead so you can build as many as possible. Force your opponent to build many mine clearers. In a game I am currently in, I have held off a power with 3 times my mineral resources just by putting so many mines over every planet. He can now clear my mines, but he had to delay his offensive about 15 turns. With the cheap mine strategy, you must watch any unit limits that might be imposed in the game.

Another thing you can do is mine some of your planets heavily and some lightly just to show mines to any scouts who come snooping to see if you have any. Defend the lightly mined ones with fighters and WPs.