Ship Settings

I've never used the guard, sentry or auto-attack settings, so I don't know anything about them. However, if you place a fleet on top of a starbase then any attacker will first have to take out the fleet before attacking the starbase. This is also true for any combination of fleets and individual ships in the same parsec. Any attacker must take out each fleet in order of the strongest first. Thus a top line attack fleet will "protect" a fleet of transports or construtors or anything else in the same parsec.

I usually set my starbase defense fleets on guard. It works pretty well as far as them not aggravating you to move every turn, but when you are at war they will go off of guard if an enemy comes near enough. In sentry though, I don't use it as they reset every time something comes in sensor range it seems.