[Suicide Junkie]

P&N had some of the heaviest mines be detectable with gravitic sensors.

The biggest problem with mines, though, is the all-or-nothing-ness of it:
Either you bring enough sweepers to clear any field with no damage, or you forget/lack tech and your fleet gets vaporized.

Tossing minesweepers in the trash, and then reducing mine warhead damage and/or mines-per-sector limits is a better way to go.
Thusly, when you place mines, they:
- WILL do some damage
- WON'T wipe out decent sized fleets
- WILL slow those fleets down while they repair the damage.

You can even set things up such that players will have to place their mines not just stacked way up on the warppoints, but spread across a number of sectors around the warppoints and planets.

The armored fleet with repair ships will still get through, but they will be slowed down to a sector or two per turn while they plow through your mined territory.