Best way to use mines:
Spread them apart, around buildings, but in such a way that a skulk can't get to a building without wall walking (which 90% never think to do).
Mines are NOT complete base defense, nothing is, but a good comm can hop out once mines are detonated and finish any resistance.
Mines are a deteral. If aliens find elec TF, they leave base alone. If they find unelec TF with turrets, they find the blindspot. They run in, see no TF, then blow up and wonder why, they stay away because of mines. Once mines blow, you replace them ONCE, and when that skulk sees the mines again, he'll either
A ) Slowly navigate the mines, which means he should be found quickly as a good marine team is moving and dying in the field actively, so the respawner will shoot him.
B ) He'll think it's not worth the time to navigate and head out.
If you are using mines, ALWAYS bind your IP's to a squad (or other key buildings), then you'll see them flashing up top when under attack and have a faster response.
Last point, if your marines are too busy humping the armory to see the incoming skulk, they deserve to go boom. If you hear/see a skulk, MOVE AWAY FROM BUILDINGS. If you hear fellow marines shooting in base, MOVE AWAY FROM BUILDINGS.
Thank you for your time. Class dismissed.
PS. I like it when I see a TF in base, I know the marines are now behind on res and upgrades. When I see unelec TF with turrets, I'm ecstatic, because I know there's a blindspot somewhere (my fav is the arms lab, yum).