[Paul1980au]

With mines it becomes so easy - just keep laying them at key warppoints and they keep flying their ships into them. When they lose a large number at once its invasion time.

Cloaked minelayers are even better - with quatum generator (unlimited fuel) and a well hiden shipyard with cargo space ie genearate mines in nearby nebula then youre cloaked mine layers can restock there instead of traveling back to one of youre planets.

Same can be useful for generating invasion fleets - having said ship fall through a spatial anomoly is also fund - invade from other side of map.

another rule is to protect key systems with several layers of mines around warp points ie a grid of 3 by 3 incorparating said grid - the enemy gets really confused.